US Entry into the Korean War: Origins, Impact, and Lessons

ABSTRACT This article describes the reasons for the outbreak of the Korean War and US entry into the conflict. At the end of World War II, the United States and the Soviet Union divided Korea into two zones of military occupation. Cold War discord between the two nations blocked agreement to end the division, resulting in formation of two Korean governments each bent on reunification. Soviet Premier Joseph Stalin reluctantly supported the Democratic People’s Republic of Korea’s invasion of the Republic of Korea on 25 June 1950 after Kim Il Sung persuaded him that victory would be quick and easy. President Harry S. Truman immediately saw the attack as the first step in a Soviet plan to use military means to achieve global dominance, but he initially ordered limited US military intervention, maintaining a prewar policy of qualified containment in Korea. When the Republic of Korea failed to halt the invasion, he sent US ground forces to prevent the Communist conquest of the peninsula. Truman wanted to avoid another world war and did not consider use of atomic weapons until China intervened. This article concludes that resumption of the Korean War is unlikely because of the US treaty commitment to defend the Republic of Korea and the weakness of the Democratic People’s Republic of Korea.

Significantly, however, saving the people of the ROK from Communist domination and attempting to reunite Korea under a democratic government was not part of the president's initial reasoning. In fact, Truman's primary reasons for deploying US military power in the Korean War had little to do with advancing and protecting the interests of Korea and its people.
Recent history had taught Truman and his advisors the axiomatic lesson that avoiding appeasement was vital to preserving the security of the United States (May 1975, 73-74, 80-82). On 27 June 1950 just two days after the DPRK's attack, his focus was on global concerns when he stated that "communism has passed beyond the use of subversion to conquer independent nations and will now use armed invasion and war" (Truman 1950a). The same set of beliefs dictated the advice that he received from both his major diplomatic and military advisors. If the United States allowed the Communists to conquer the ROK, US leaders were certain that the Soviet Union would stage new acts of aggression, most likely in Europe. This fear motivated a major reversal in US policy toward Korea, as before the DPRK's attack, the United States was indifferent to the fate of the ROK (May 1975, 79;Spanier 1965, 17-20;Berger 1957, 182;Rees 1964, 446). However, Truman's response to the Korean crisis was in reality entirely consistent with a postwar policy that judged preventing Communist domination of all Korea as a central factor in protecting larger US security interests. His strategy sought to build the ROK's capacity for self-defense, removing the need for a positive guarantee of military protection. When the DPRK attacked, Truman waited for almost one week before abandoning his limited approach and committing ground forces in the Korean War (Matray 1978).
Korea would have emerged from World War II as a united nation, likely under the control of a Communist government, had Truman not gained Soviet approval for dividing the peninsula at the 38 th parallel into two zones of military occupation (Matray 1981). Thereafter, existing political and economic distress in southern Korea increased, causing the War Department to apply tremendous pressure for immediate US military withdrawal. But the State Department objected, fearing that doing so would lead promptly to Communist domination over all of Korea and thereby inflict serious damage to US international credibility and prestige. Meanwhile, Soviet-American negotiations to resolve the Korean dispute collapsed because of the inability to agree on a group of Korean leaders that would comprise a government for a united Korea. To resolve his dilemma, Truman instructed Secretary of State George C. Marshall to place the Korean issue on the agenda of the United Nations, which he did in a speech on 17 September 1947. He also approved planning for US military withdrawal (Matray 1985, 99-123).
On 14 November 1947 the UN General Assembly approved a resolution calling for Korea's reunification after internationally supervised national elections. The Truman administration, anticipating that the Soviet Union would refuse to cooperate, had shifted its policy to pursuing creation of a separate government in southern Korea capable of defending itself. While the United States provided military and economic aid, a stamp of legitimacy from the United Nations would enhance further a separate ROK's chances of survival. Early in 1948, the United Nations, under intense American pressure, agreed to supervise elections in the south alone in May for representatives to serve in a legislative assembly and later certified the results as valid. 1 In August 1948, US military occupation of the ROK ended with the inauguration of the Republic of Korea (ROK). The next month, the Soviet Union responded in kind, sponsoring creation of the Democratic People's Republic of Korea (DPRK). While President Syngman Rhee constructed a repressive, dictatorial, and anti-Communist regime in the south, Premier Kim Il Sung emulated the Soviet model for political, economic, and social development in the north. Both leaders were determined to unify Korea. These events magnified the need for US withdrawal, since Soviet Premier Joseph Stalin, acting on the DPRK's request, announced that Soviet troops would leave the north by the end of 1948 (Matray 1985, 164-67).
By then, the Truman administration had taken steps to provide the ROK with the ability to defend itself against anything less than a full-scale invasion. For example, a US Army advisory team had trained and equipped an army cadre of 25,000 men in the south and supervised the formation and training of a National Police Force. But despite internal security forces and the continuing presence of US troops, the new government immediately faced violent internal opposition, climaxing in October 1948 with the Yosu-Sunchon Rebellion. Despite plans to leave the ROK before the year ended, Truman delayed withdrawal until 29 June 1949. At that time, he believed that the ROK could survive and prosper without direct US military protection from US troops. The prior April, Truman had approved National Security Council (NSC) Paper 8/2, providing for the submission to Congress of a three-year economic assistance request for the ROK that totaled $540 million (about $6 billion in 2021 dollars). It also included a commitment to train, equip, and supply a security force of 65,000 with enough strength to deter a DPRK attack (Matray 1985, 168-85). In Korea, containment relied on economic aid, technical advice, and limited military assistance (Gaddis 1977, 283-84;William, Kaplan, and Coblenz 1956, 2). Truman and his advisors accepted as valid the crucial assumption that Moscow would not resort to open armed aggression to expand the area of Soviet control, but instead would continue to depend primarily on the tactics of infiltration and subversion (Acheson 1951;Kennan 1967, 485).
Significantly, Truman expected his policy of qualified containment to achieve peaceful rollback of communism in Korea, as he indicated on 7 June 1949 when he appealed to Congress to approve a Korean aid package, declaring that South Korea has become a testing ground in which the validity and practical value of the ideals and principles of democracy which the Republic [of Korea] is putting into practice are being matched against the practices of communism which have been imposed upon the people of north Korea. The survival and progress of the Republic toward a self-supporting, stable economy will . . . encourage the people of southern and southeastern Asia and the Islands of the Pacific to resist and reject the communist propaganda with which they are besieged. Moreover, the Korean Republic, by demonstrating the success and tenacity of democracy in resisting communism, will stand as a beacon to the people of northern Asia in resisting the control of the communist forces which have overrun them (Truman 1949). Meanwhile, US military advisors supervised a dramatic improvement in the ROK Army. In fact, they were so successful that confident ROK officers started to initiate attacks northward across the 38th parallel during the summer of 1949. These assaults ignited border clashes with DPRK forces, often involving battalion-sized units (Merrill 1985, 130-51). A kind of war already was underway in Korea before 25 June 1950. Fearful that Rhee planned on launching an offensive to achieve reunification, the Truman administration limited the ROK's military capabilities, denying requests for tanks, heavy artillery, and warplanes.
Containment in Asia, with its reliance on local self-defense and limited US aid, was consistent with the priority Truman placed on reducing the federal budget. But Congress was not eager to finance even this limited strategy. New Secretary of State Dean G. Acheson and other officials, for example, lobbied heavily in support of the threeyear aid proposal for Korea, but without success. Most congress members thought the ROK was too unstable to survive, while Jiang Jieshi's (Chiang Kai-shek's) supporters assailed the administration's readiness to help Rhee's regime, while also denying economic aid to the Guomindang government in Taiwan. Acheson was trying to build political support for assistance to Korea when on 12 January 1950 he presented an optimistic assessment of the ROK's future in an address at the National Press Club. One week later, the House of Representatives defeated the bill by one vote. Truman, determined to gain passage, submitted a revised bill reducing the first-year cost of the plan to $100 million. As an important addition, the Far Eastern Economic Assistance Act included limited aid for Jiang's China, gaining congressional approval in February 1950. In June, Congress consented to another bill that appropriated $100 million for the plan's second year (Matray 1985, 219-21).
Acheson's National Press Club speech became notorious because he excluded both the ROK and Taiwan from the American "defensive perimeter" in the Pacific. If attacked, he stated, the ROK would have to rely first on the United Nations. Six months later and thereafter, critics would charge that Acheson gave the Communists a "green light" to launch an invasion. Soviet documents have revealed, however, that Acheson's words had no impact on Communist planning for the invasion (Matray 2002a). Debate over whether Acheson invited the DPRK to attack has diverted attention from the more important part of the speech that referred to Korea as an area where the United States was providing limited help and thereby fostering the emergence of a strong democracy. In Korea, Acheson explained, there existed "a very good chance" for successful resistance to Communist expansion and it did not require an express guarantee of US military protection. The administration's strategy would succeed in the ROK, he reasoned, because, in contrast to China, the ROK not only wanted American aid but would use it effectively. Acheson highlighted the importance of the ROK in Truman's strategy of qualified containment in Asia when he concluded that "we have a greater opportunity to be effective" in Korea than anywhere else on the Asian mainland (Acheson 1950).
By June 1950, the US policy of containment in Korea through economic means appeared to be experiencing marked success. First, the ROK had acted vigorously to halt spiraling inflation. Second, elections in May had given Rhee's opponents control in the legislature. Third, the ROK army had virtually eliminated leftist guerrilla operations threatening internal order. In response, the State Department proposed an increase of six million dollars in military assistance to the Korean army and coast guard. Truman agreed with the State Department's judgment that the DPRK's ability to defend itself was important for US security, justifying an increase in its military capabilities. On 1 June 1950 the president addressed Congress and requested several million dollars in military aid for the ROK as part of the Mutual Defense Assistance Program. In his speech, Truman employed globalist rhetoric, emphasizing that Moscow's determination to dominate the entire world was clear. However, his strategy for countering Soviet expansionism, he explained, focused on providing economic aid, relying on the United Nations, and creating local military strength. Free nations, the president insisted, could withstand the Communist challenge if they received enough military aid from the United States to make self-defense possible (Truman 1950b). At that moment, the ROK was not vital to US national security, but a global rationale was in place to make its survival imperative.

DPRK Attack and US Response
At 9:26 p.m. on 24 June 1950 Truman, who was vacationing in Independence, Missouri, received a telephone call from Acheson informing him that DPRK forces had staged a full-scale military invasion of the ROK. They agreed that the president would not return until the next day and the State Department would proceed with plans to refer the matter to the United Nations. This latter decision was entirely consistent with past American policy. US Department of the Army contingency plans provided for such action in the unlikely event of a DPRK assault. In his Press Club speech, Acheson also stated that if open military aggression occurred beyond the US "defensive perimeter", "the initial reliance must be on the people attacked to resist it and then upon the commitments of the entire civilized world under the Charter of the United Nations". 2 Truman and Acheson were in complete agreement that the United States should provide assistance to the ROK only under the auspices of the United Nations. 3 A desire to avoid the direct and unilateral application of US military power explains in part the administration's decision to request action at the Security Council. Truman believed that United Nations support for the ROK would bolster morale in the ROK and greatly improve the ability for local self-defense.
Abundant evidence exists supporting the conclusion that Truman, from the start of conflict, viewed the Korean War from a global perspective, making frequent references to the necessity of preventing the collapse of the United Nations and avoiding a new world war (Leffler 1992, 361;Hamby 1995, 535-37;Stueck 1995, 43-44). As for the ROK itself, the United States had to intervene to uphold its global credibility and prestige because along with the United Nations, it had sponsored creation of the ROK (Stueck 1981, 186;Ferrell 1983, 115;MacDonald 1986, 30). Truman and his advisors were convinced that the Soviet Union had ordered the DPRK's attack, but initially feared that its purpose was to divert US attention prior to a military assault in Europe. They certainly never considered that the North Koreans might have their own reasons for using military means to reunite their nation. Soviet documents have provided unequivocal evidence that the DPRK, contrary to its continuing denials, was responsible for launching a longplanned invasion.
During 1949, Stalin consistently had refused to approve Kim Il Sung's persistent requests to authorize an attack on the ROK. He believed that the DPRK still lacked military superiority over the ROK. That fall, however, the Communist victory in China placed pressure on the Soviet leader to show support for the same outcome in Korea. In January 1950, Stalin in fact discussed Kim Il Sung's plans with him personally in Moscow, but he was not ready to give final consent. At that time, he did authorize a major expansion of DPRK's military capabilities. When they met again in April, Kim Il Sung persuaded Stalin that military victory would be quick and easy, largely because of support from southern guerrillas and an expected popular uprising against Rhee's regime. Stalin still feared US military intervention, advising Kim Il Sung that he could stage his invasion only if China's Mao Zedong approved. In May, Kim went to Beijing to gain Chinese consent. Significantly, Mao Zedong also voiced concern that the United States would act to defend the ROK, but he gave his reluctant approval as well (Matray 2002a, 39-48).
Reports from the ROK immediately following the attack cast serious doubts on whether the United States could limit its involvement in the conflict. John J. Muccio, US ambassador to the ROK, cabled Washington that "the North Koreans are engaged in an all-out offensive to subjugate South Korea". "Future course of hostilities", he sternly warned, "may depend largely on whether [the] US will or will not give adequate assistance". General Douglas MacArthur, the US occupation commander in Japan, also emphasized that the situation was grave and might require American military intervention when he requested authorization to send more supplies to the ROK. 4 In Moscow, US diplomatic representatives were more vehement in urging Washington to adopt a decisive course of action. The Embassy staff members insisted that "this aggressive DPRK military move . . . represents clear-cut Soviet challenge which in our considered opinion US should answer firmly and swiftly as it constitutes direct threat to our leadership of free world against Soviet Communist imperialism". Any delay, the cable warned, only would hasten the collapse of the ROK and encourage Stalin to embark on similar adventures elsewhere. If the United States acted quickly and with resolve, however, Moscow might forsake further aggressive action. 5 Despite such advice, US policymakers emphasized restraint on the morning of 25 June in searching for an appropriate response to the crisis. For example, the State Department formulated a list of policy alternatives that included such limited options as sending the ROK all essential equipment and permitting American advisors to remain with the ROK army. If necessary, the United States would utilize naval and air power to establish a protective zone around the ROK capital at Seoul for the evacuation of American personnel. If the ROK's survival demanded drastic action, the United States might deploy ground forces to "Stabilize [sic] the combat situation including if feasible the restoration of original boundaries at 38 degrees parallel". Significantly, the State Department recommended that MacArthur immediately dispatch a survey team to the ROK to determine the minimum amount of assistance required to enable the ROK to defend itself without weakening the security of Japan. 6 That evening, Truman, having returned to Washington, discussed these recommendations with his top advisors at Blair House, where he was living while the White House was undergoing renovation. During dinner, those present agreed quickly that the DPRK's attack was equivalent to Hitlerite aggression, and that appeasement was not a viable alternative. But many also voiced concern that if the Communists were unable to subdue the South Koreans, the Soviet Union or China might enter the conflict. All those leaders present expressed the hope that the ROK could defend itself without drastic American assistance. 7 After dinner, Acheson summarized the State Department's recommendations. He suggested, in addition, that Truman order the Seventh Fleet into the Taiwan Strait to prevent an attack on either Taiwan or the Chinese mainland. General Omar N. Bradley, chair of the Joint Chiefs of Staff (JCS), immediately supported State's proposals. The United States, he stressed, had to draw a line against Soviet expansionism sometime and Korea "was as good an occasion . . . as anywhere else". But Bradley advocated only the use of American air and naval power to halt the DPRK's advance. He opposed deploying American ground forces in Korea because he did not believe that Moscow wanted war with the United States. Naval Chief of Staff Admiral Forrest Sherman joined Bradley in stressing the importance of avoiding a complete commitment of US power. He favored an increase of American advisory personnel in the ROK and reliance on air power to delay the Communist advance. Air Force Chief of Staff General Hoyt S. Vandenberg then reminded his colleagues that, while a limited approach was feasible, the United States was not prepared to counteract Soviet military power if Stalin chose to enter the conflict. Frank Pace, Francis Matthews, and Thomas Finletter, the secretaries of the Army, Navy, and Air Force respectively, all agreed that, in the absence of Soviet military intervention, US air power was sufficient to preserve the ROK's survival. Truman's civilian advisors all stressed the need for some kind of prompt action but were unanimous in opposition to the use of combat troops as well 8 Such advice only reinforced Truman's inclination to adopt a restrained approach in his initial response to the Korean crisis. He decided to approve the shipment of all necessary supplies to the ROK, the dispatch of a survey team to Seoul, and the transfer of the Seventh Fleet from the Philippines to Japan. He also instructed the Air Force to prepare plans for the destruction of all Soviet air bases in Asia; the State and Defense Departments would formulate contingency plans for responding to the next probable location of Soviet aggression. The president ordered his advisors to stress that the United States was acting under the authority of the United Nations and would limit its military involvement to protection of American evacuation from the ROK. 9 Truman and his advisors manifested a clear reluctance to take extreme action in the immediate hours after the DPRK assault. Although they perceived in the invasion a Soviet design for world conquest, they sought to counter the threat through relying on limited means. Such a reaction was hardly surprising, since the main thrust of US postwar policy was restraint. Washington would commit its naval and air power alone, thus avoiding the momentous step of dispatching combat troops (Figure 1) 10 7 Acheson Comments, 13 February 1954, Princeton Seminars Transcripts, reel 2, tape 1, page 3, Acheson Papers, HSTL; Collins (1967, 13); Smith (1951, 78-79 Truman (1956, 334-35); Acheson (1969, 406); Collins (1967, 14); Schnabel (1972, 69 However, Truman's determination that the DPRK's attack replicated Axis aggression during the 1930s meant he would not allow the conquest of the ROK. If the DPRK threatened to overrun the peninsula, global assumptions would demand a near complete commitment of US power and prestige in the struggle to ensure the survival of the ROK. At this first Blair House meeting, Truman also affirmed the State Department's action earlier that day to refer the Korean crisis to the UN Security Council, which had resulted in passage of a resolution calling for a ceasefire and DPRK withdrawal. Despite this show of concern, ROK forces were unable to halt the advance of the Korean People's Army (KPA) and the battlefield situation continued to deteriorate. On the night of 26 June, Truman convened a second meeting at Blair House. Acheson again opened the discussion and recommended the removal of all restrictions on the use of naval and air power in Korea. The president approved the proposal immediately but emphasized that American operations would not extend north of the 38 th parallel (Figure 2). The secretary of state then raised the issue of Taiwan. Truman now decided that the Seventh Fleet should move into the Taiwan Strait. After a brief discussion of future policy at the United Nations, US Army Chief of Staff Collins summarized the battlefield situation in Korea. The ROK, he pessimistically reported, was on the verge of complete collapse. Acheson argued that if Korean efforts at self-defense failed, the United States had to intervene more directly. Truman declared, somewhat vaguely, that "we must do everything we can for the Korean situation for the United Nations". Bradley and General J. Lawton Collins, the US Army Chief of Staff, assuming that Truman had just indicated willingness to commit combat ground forces, reminded him that such a decision would entail the need for full mobilization. In response, both Truman and Acheson voiced the hope that the United States still could avoid this drastic step 11 Some writers have claimed that by then, Truman had decided to dispatch US combat forces to Korea. They point, for example, to his decisions at the second Blair House meeting that the United States, to demonstrate its resolve, would strengthen its forces in the Philippines and provide more aid to the French to fight the Communists in Indochina (Lowe 1986, 162;Kaufman 1986, 30). Yet Truman also stated emphatically that "I don't want war". His decisions at the second Blair House meeting in truth represented only a minor change in tactics. American air and naval power remained the basic ingredients in the nation's response in Korea. The president continued to place his confidence in the ROK's ability to defend itself with limited amounts of US assistance. Collins transmitted new instructions to Tokyo authorizing MacArthur to "offer fullest possible support to ROK forces so as to permit these forces to reform". Washington thus sought to avert the collapse of the ROK with less than a complete commitment of US military power 12 A major reason for the administration's hesitancy in the period immediately after the attack was anxiety about the possibility of Soviet military intervention in the conflict. US policymakers opposed the use of American ground forces partially out of fear that such action would force the Soviet Union to intervene militarily as well. Ironically, Truman and his advisors were equally apprehensive that in the event the ROK successfully defended itself, Moscow might feel obliged to assist its Communist client in completing the conquest of the peninsula. 13 Oddly, they were far less concerned about Chinese intervention.
On 27 June, the UN Security Council passed a second resolution calling upon members to provide assistance in defending the ROK. The United States, however, had acted before receiving the UN request. Indeed, Truman had told Acheson after the first Blair House meeting that if the United Nations had not acted, he would have taken steps to help the ROK anyway. But these actions had no apparent impact on delaying the DPRK military offensive, as the KPA captured Seoul (Figure 3). Cables from American representatives in the ROK indicated that ROK government leaders were becoming "seriously dispirited" as their army continued to retreat. On 28 June, General John H. Church, as head of the survey team, reported to MacArthur that only American combat forces could prevent the demise of the ROK. 14 Later that day, the NSC convened to consider the deepening crisis, with discussion focused on the issue of possible Soviet participation in the war. US leaders agreed that the administration's decision to assist in the defense of the ROK did not entail a commitment to engage in war with the Soviet Union. Acheson voiced pointed concern that in the event of Soviet military intervention, Washington, not MacArthur, should maintain total control over events in Korea. Truman concurred. The president then ordered the JCS to inform MacArthur that "if substantial Soviet forces actively oppose present operations in Korea, United States forces should defend themselves, should take no action to aggravate the situation and should report the situation to Washington". 15 Evidently, Truman wanted to retain the freedom to reconsider his decision to punish the aggressors in Korea and allow conquest of the ROK if an open military clash with the Soviet Union was the price of US involvement.
On the morning of 29 June, General MacArthur landed at Suwon in the ROK for a personal survey of the situation. While enroute, he authorized bombing missions north of the parallel, although his instructions specifically prohibited such action. After lengthy discussions with Muccio and President Rhee, MacArthur drove northward to observe the fighting south of Seoul. He concluded that the ROK's position was indeed desperate 14 Everett F. Drumright to Acheson, 29 June 1950FRUS, 1950Schnabel (1972, 74). 15 Acheson to Louis A. Johnson, 28 June 1950, FRUS, 1950Major General Richard Lindsay Memorandum, 28 June 1950, RG 218, CCS 383.21 Korea (3-19-45), Section 21, NA; Truman (1956, 340-41). (MacArthur 1964, 332;Collins 1967, 18-19;Appleman 1961, 44-45 June press conference, Truman still thought a limited commitment was possible, agreeing with a newsman's description of the war as a "police action". Later, this characterization seemed to trivialize the conflict and allowed critics to label it "Mr. Truman's War" (Matray 2012, 508). At the White House on the afternoon of 29 June, Truman's remarks to his top advisors were indicative of his continued emphasis on a cautious approach: We must be damn careful. We must not say that we are anticipating a war with the Soviet Union. We want to take any steps we have to push the North Koreans behind the line . . . but I don't want to get us over-committed to a whole lot of other things that could mean war.
Secretary of Defense Louis A. Johnson voiced support for Truman's position. He informed the president, however, that the JCS believed it was essential to establish a beachhead in the ROK in case the complete evacuation of American personnel became necessary. Truman approved the proposal but reminded Johnson that US military involvement sought to do no more than "keep the North Koreans from killing the people we are trying to save". 18 Acheson's comments reflected similar concern over the danger that an escalation of hostilities might draw the United States into a major conflict. While expressing approval for MacArthur's decision to launch air strikes north of the parallel, he pointed to the danger of flights into Manchuria. At the same time, Moscow's public posture of neutrality had removed many of Acheson's misgivings about the wisdom of a complete commitment of US power in defense of the ROK. He declared that, if necessary, the United States should use ground forces. "It would be a great disaster", Acheson argued, "if we were to lose now". Truman shared his opinion that Moscow did not want a direct military clash with the United States in Korea, stating prophetically that "the Russians are going to let the Chinese do the fighting for them". 19 That evening, Washington dispatched new instructions to MacArthur authorizing him to employ "such army combat and service forces as to insure the retention of a port and air base in the general area Fusan-Chinhae". In addition, MacArthur could engage purely military targets north of the parallel if such action was essential for the reduction of ROK casualties. "Special care will be taken", the JCS stressed, "to ensure that 16 Acheson Briefing Book Notes, 29 June 1950, Box 71, Korea (29 June 1950, Elsey Papers, HSTL; MacArthur to JCS, 29 June 1950, RG 6, Box 2, Korea File #1, MacArthur Papers, DMML. 17 Alan G. Kirk to Acheson, 29 June 1950, FRUS, 1950 Memorandum of Conversation, 29 June 1950, FRUS, 1950Truman (1956, 34, 142); Elsey Notes, 29 June 1950, Box 71 (White House-State-Defense Meeting, 5 p.m., 29 June 1950), Elsey Papers, HSTL. 19 Ibid; Acheson (1969, 411-12). operations in the DPRK stay well clear of the frontiers of Manchuria or the Soviet Union". Washington reminded MacArthur that the United States sought to avoid war with the Soviet Union. The administration's instructions concluded that if the Soviets intervened militarily, American forces should implement defensive measures alone and MacArthur should report the situation to Washington without delay. 20 But these limits on US military intervention in the Korean War ended on the morning of 30 June when the JCS received MacArthur's official report of his inspection of the ROK contradicting his earlier optimistic assessment. In all probability, his receipt while preparing his report of extremely pessimistic news from General Church about the continued retreat of ROK forces determined the contents of MacArthur's message. Indeed, the general reported that the situation had deteriorated further, and the ROK army could not halt the Communist advance because it was in a state of utter confusion, which made effective resistance impossible. The DPRK's army, by contrast, was well trained and well equipped, possessing some of the best combat units MacArthur had ever seen (Figure 4) (Paige 1968, 239;Appleman 1961, 56-57).
MacArthur placed the Korean crisis in a frightening global context before making his stunning recommendations. "It is now obvious", he exclaimed, "that this force has been built as an element of Communist military aggression". Since the ROK's army was no match for such a force, MacArthur predicted that the DPRK's conquest of the entire peninsula was probable. His report concluded that the situation demanded drastic action. He observed dramatically that "the only assurance for the holding of the present line, and the ability to regain later the lost ground, is through the introduction of US ground combat forces into the Korean battle area". MacArthur recommended that the JCS secure immediate presidential authorization for the dispatch of one Regimental Combat Team to the front line and the introduction of two additional divisions as soon as practicable for use in a counteroffensive. In the absence of full use of US power, MacArthur warned, military operations would be either "needlessly costly in life, money, and prestige" or even "doomed to failure". 21 Washington received MacArthur's report with shock and dismay because his prior assessment indicated that it could avoid commitment of ground troops. Collins cabled Tokyo that a decision of such magnitude required time for discussion and analysis. He asked MacArthur if the instructions of the previous night were not sufficient to meet the situation temporarily. MacArthur replied that these orders did not provide enough latitude for effective action. "Time is of the essence", he declared, "and a clear-cut decision without delay is imperative". 22 Collins contacted Secretary of the Army Pace immediately and informed him of MacArthur's recommendations. At just before five o'clock on the morning of 30 June, Pace phoned the president and apprised him of the situation. Truman's initial reaction seemed to indicate a continuing desire to avoid extraordinary action. "Do we have to decide tonight?" he asked. Pace proceeded to inform the president that, in MacArthur's judgment, the ROK was on the verge of complete collapse. In response, Truman decided to approve the commitment of one Regimental Combat Team, but he deferred action on the use of two combat divisions until later that morning. 23 Several hours later, the president convened a meeting of his major advisors to discuss MacArthur's request. The most recent report from Tokyo confirmed that the ROK's army was in shambles, its people demoralized, and its government near disintegration. 24 After soliciting opinions, the president found that a consensus existed on the necessity to remove all restrictions on the use of US combat ground forces in the ROK. Truman therefore approved MacArthur's request. 25 There can be no doubt that MacArthur's emphatic request for authority to use US combat ground forces was the crucial element in the president's decision. Truman removed the final restrictions on the US commitment to defend the ROK only after MacArthur had reported that the ROK was totally incapable of defending itself and preventing Communist conquest of the peninsula.
Subsequently, Truman falsely portrayed US military intervention in the Korean War as part of a real collective security operation. On 7 July, the UN Security Council passed a resolution approving the creation of the United Nations Command (UNC) and calling on Truman to appoint a UNC commander, who immediately selected MacArthur for the job. The UNC commander was required to submit periodic reports to the United Nations on developments in the war. Truman had vetoed a proposal for the creation of a UN committee having direct access to the UNC commander and instead approved a process whereby MacArthur received instructions from and reported to the JCS through US Army Chief of Staff Collins. Since Washington had to approve them, MacArthur's reports to the United Nations in fact were after-action 21 MacArthur to JCS, 30 June 1950, FRUS, 1950, 7, pp. 248-50. 22 Teleconference, 30 June 1950, FRUS, 1950Memorandum, 30 June 1950, Box 71, Korea (30 June 1950, Elsey Papers, HSTL. 23 Pace, Oral History Interview Transcript, 22 January 1972, HSTL, pp. 73-74. See also, Truman (1956; Paige (1968, 256). 24 Truman (1956, 343); William J. Sebald to Acheson, 30 June 1950, FRUS, 1950, 7, pp. 254-55. 25 Elsey Notes, 30 June 1950, Box 71, Korea (30 June 1950, Elsey Papers, HSTL; George M. Elsey, Oral History Interview Transcript, 9 April 1970, p. 270, HSTL. summaries of information that was common knowledge because newspapers already had printed coverage of the same developments. Although fifteen other nations committed military units to defend the ROK, the United States and the ROK contributed ninety percent of the manpower. Moreover, the United States provided the weapons, equipment, and logistical support to those nations helping to save the ROK (Matray 2002b, 111). While Truman and his advisors believed that nothing less than the future peace and security of the international community was at stake in Korea, few nations who fought with the United States were as certain. Ultimately, Truman's reasons for acting to save the ROK after the DPRK staged its invasion on 25 June 1950 had little to do with his concerns about Korea or its people. His decision to commit US combat troops in the Korean War was largely the product of his perception that the struggle was analogous to events in the 1930s. However, he did not believe that a near total commitment of American military power was necessary until several days after the outbreak of the conflict. If Truman had determined within hours after the invasion that the ROK's survival was a vital US security interest, he would have sent combat troops to the peninsula immediately to crush the aggressor and show the extent of US resolve. Instead, Truman referred the matter to the United Nations and maintained confidence in the ROK's ability to defend itself. His Korea policy before the DPRK attack explains his reluctance to dispatch American combat ground forces to the ROK. Containment in Korea (and elsewhere in Asia with the exception of Japan) sought to counter the Soviet threat with a limited commitment of US power. Its central objective was to develop the political, economic, and military strength of the ROK so that it could defend itself. If the ROK had been able to repel the Communist assault alone, it is possible that the Truman administration would have gained renewed confidence in this strategy and continued a limited approach.

Implications of Current US Commitment to Protecting the ROK
William Stueck has made the compelling argument that if the United States had made clear the extent of its commitment to protect the ROK before 25 June 1950, there would have been no Korean War (Stueck 1981, 171). More than seventy years later, no chance exists that history will repeat itself in Korea because the United States has made it clear that it will respond to a new DPRK assault on the ROK with all of the military might at its disposal. There are at least three reasons confirming a belief in the completeness of the US commitment to defend the ROK. First, US military forces remain deployed in the ROK -unlike in June 1950 -and they would sustain casualties in the event of a DPRK attack, guaranteeing massive American military retaliation. Second, the United States has a legal obligation to defend the ROK if the DPRK attacks under the 1954 US-ROK Mutual Security Treaty. Third, an alliance "forged in blood" has strengthened over the past seven decades as Americans have gained respect for South Koreans as effective fighters and builders of a modern nation (Stueck and Yi 2010). Whether the United Nations would join the United States in defending the ROK during a new Korean War would depend on how the conflict began. In 1990, President George H. W. Bush received enthusiastic support from the international organization in waging a war to punish Saddam Hussein for an act of blatant aggression. By contrast, the United Nations refused to endorse the second US war against Iraq. More recently, it has approved US-backed resolutions imposing economic sanctions on the DPRK to end its nuclear and missile testing.
A new Korean War is improbable in any event because the DPRK no longer contemplates an attack on the ROK, not least because there is no Soviet Union to provide the DPRK with the weapons and supplies it would need for a serious offensive. Moreover, the People's Republic of China (PRC) would not support a military assault and probably would withhold the oil that the DPRK would need to sustain an invasion. Aside from these constraints, the DPRK's conventional military capabilities simply are not sufficient to overwhelm the ROK. The DPRK has an enormous army, but it is equipped with antiquated weapons. It also lacks fuel for its armored vehicles, tanks, and aircraft (McCormack 2004, 107). Moreover, "Pyongyang's end game has changed from . . . unification", Victor Cha and David Kang emphasize, "to basic survival" because it faces a superior adversary (Cha and Kang 2003, 20-21). The ROK has a far stronger economy that has made possible much higher military spending. For example, in 1998, it spent two times more on defense than Pyongyang, although this constituted just 3.5% of its budget as compared to 37.9% in the DPRK. In addition, the ROK has cutting-edge weaponry and sophisticated communications, intelligence, and electronic warfare capabilities (Bleiker 2003, 735;Niksch 2006, 109-110).

Lessons from the Korean War about the Use of Nuclear Weapons in Future Conflicts
Soviet possession of atomic bombs in June 1950 played no role in the start of the Korean War and therefore the DPRK's attack on the ROK provides no analogs for how nuclear weapons might motivate a current nation to initiate a conflict. However, because neither Pyongyang nor Beijing had nuclear weapons during the Korean War, the United States could consider using atomic bombs at a few key moments as the war unfolded. For example, Truman at a press conference in late November 1950 after massive Chinese intervention stated that the United States had use of atomic bombs under consideration since the start of the war. This frightened US allies in Western Europe, who registered strong opposition to using nuclear weapons in Korea. Yet, the Truman administration continued to prepare to use them, especially just before the huge Communist offensives in April and May 1951, as well as thereafter. Although the threat to US troops never was sufficient for the Truman administration to use atomic bombs, worries about US allies withdrawing from Korea would have made it difficult to do so. During the spring of 1953, President Dwight D. Eisenhower developed plans for nuclear attacks on China and conveyed them to the Communists to intimidate them into accepting favorable terms for an armistice. However, his sensitivity to opposition from US allies to using atomic bombs argues against him implementing his plan. Events during the Korean War suggest that a nation acting alone in a future war would be more likely to use nuclear weapons than one wanting to maintain the support of allies.
Unlike during the Korean War, the DPRK now possesses nuclear weapons and missiles to deliver them. Moreover, it has demonstrated regularly since the signing of the Korean Armistice its willingness to act unilaterally. However, Pyongyang has not developed nuclear weapons capabilities as part of plans to initiate a war but, instead, to deter a US-ROK attempt to destroy the DPRK that almost succeeded in the fall of 1950.
As for other nations, the DPRK provides little guidance for what to anticipate regarding their possible use of atomic weapons in the initiation or conduct of the conflict because its situation is unique. Most obviously, Pyongyang understands that a nuclear attack on the ROK would ignite a blistering counterattack resulting in its annihilation. Just as important, however, it would make it impossible for enraged South Koreans to fulfill the DPRK's expectation since its inception of them welcoming reunification under its leadership. Kim Il Sung may have expected that his invasion would spark a popular uprising against the unpopular Rhee regime, but it is inconceivable that Kim Jong Un could think that South Koreans would view a nuclear attack as an act of liberation. Current nations without the motivation of national reunification and capable of unilateral action, however, might not have any qualms about using nuclear weapons to achieve goals that they see as important to advancing their national interests.