On the night of the North Korean invasion, Truman convened the first Blair House Meeting of his closest advisors. Though the meeting did not focus solely on Korea, in fact it began with a discussion of the US policy toward the Nationalist Chinese in Formosa (an issue MacArthur believed to be of great importance) Truman allowed Dean Acheson to speak regarding the Korean situation. Gen. Omar Bradley summarized the group's feelings, saying that the US would have to "draw the line" somewhere, and that Korea seemed as good a place as any. The immediate results of the Blair House Meeting were orders to evacuate American civilians from Korea, to provide military supplies to the embattled South Korean army, and to move the 7TH US Fleet into the Formosa strait, blocking the People's Republic of China from invading Formosa while the US was distracted with Korea.
MacArthur's reports grew worse over the next few days, describing the North Korean rout of ROK forces. The ROK army fled south, to the tip of the peninsula, in the direction of the port city of Pusan. On June 27, 1950 the US promised naval and air support to South Korea. Truman further hoped to discourage the Soviets or the Chinese Communists from getting involved in the war by integrating US troops into a force from the UN, and claiming the whole operation to be UN sanctioned and led.
Fleeing across the Han River Bridge, the panicky South Koreans blew the bridge before all the fleeing South Korean soldiers could get across. Hundreds died, and men and equipment were stranded on the other side. Major-General John H. Clark and ROK chief-of-staff General Chae Byong Duk consolidated what remained of their forces to establish a headquarters at Suwon. In a personally dangerous move, MacArthur flew in to Suwon and drove up to the front to see the fighting for himself. Based on his trip to the front, MacArthur cabled Washington for authority to commit ground troops. Calling his decision a "police action", Truman allowed MacArthur to move a US regiment to Pusan. Truman did not, however, immediately send to Korea the number of troops MacArthur wanted.
On June 30, with the ROK army in dire straits, Truman relented and gave MacArthur authorization to transfer 2 full divisions from Japan to Korea. For roughly two-and-a-half months, MacArthur simply tried to prevent the North Korean army from taking Pusan. Meanwhile, the US conducted a strategic bombing campaign and blockaded the coastline with warships. While Navy and Air power had little effect, MacArthur did manage to attain his main goal of holding Pusan. Also, during this delay, MacArthur was able to transform his out-of- shape occupation force into an army.
By July 4, 1950, the balance had begun to swing toward the US. On July 7, the UN asked the US to appoint a UN commander. Truman quickly made MacArthur Commander in Chief of the UN Command (CINCUNC). MacArthur responded to this honor by demanding more troops. It was not log before Truman's Korean War budget neared the tripling of military expenditures recommended by NSC- 68.
Trapped, backed into a corner against the sea, the situation continued to look bleak for the US/UN/ROK forces in South Korea. UN ground troops, under Lt.- general Walton H. Walker, commander of the UN ground troops in Korea, spent the bulk of their time working hard to build the "Pusan Perimeter", a fortress- like series of entrenchments in southeastern Korea. Still, these entrenchments offered little chance for US/UN/ROK counteroffensive. The anti-communist forces seemed stuck.
Rather than asking for a declaration of war from Congress, Truman opted to claim that he was sending ships and planes at the request of the UN. This allowed Truman, rather than Congress, to take credit for responding to the Communist threat. Indeed, Congress, the Press, and the Gallup Polls all responded very favorably to Truman's policies. One side-effect that few considered was the following: since the 7TH Fleet was barring the PRC from invading Formosa, the PRC transferred most of its army to Shantung province, a location from which it would be easy to quickly become involved in the Korean conflict.
The UN force that went to Korea was the first-ever "international peace-keeping force." But although its ideology of peace and non-aggression seem very positive, the peacekeeping force was in this case actually an instrument of the US. Only 16 countries actually sent men on the mission, and most of these were NATO countries, which were hardly neutral when it came to Communists. And the majority of the troops by a good margin were American: while 5.7 million American troops would ultimately serve in the Korean War, only about 40,000 troops from the other UN Peace-Keeping nations were involved, and of these, half were British. In fact, the tiny non-American units actually tended to get in the way and confuse American planning more than they actually helped the war effort. Chiang Kai-Shek offered 35,000 Chinese Nationalist troops, but Truman and Acheson rejected this, afraid the involvement of Chinese Nationalists might provoke the involvement of the much larger Red Army of the PRC. Clearly, the UN forces were an instrument of US policy designed to give the appearance of international consensus rather than a truly autonomous international organization.
MacArthur's call for American ground troops was based on several factors. First of all, bad weather was limiting the accuracy of air power to defend the South Koreans. Second, the ROK troops could not now be given tanks and be expected to use them: only well trained US soldiers could operate the tanks and anti-tank weapons necessary to halt the advance of the Soviet T-34s operated by North Korean fighters.
Although Truman did not immediately give MacArthur all the troops he wanted, once some ground troops were committed to Korea, it was inevitable that more would follow. Once committed in this battle against Communism, the US could not afford to lose for fear of losing its credibility with all of its allies, especially the NATO powers. The same scenario would play out a decade later in Vietnam. In this way, like a brush fire, "Limited Wars" in the modern-era often proved (and prove) very difficult to contain, to keep "limited."
The American troops MacArthur brought in from Japan had not seen fighting in years, if ever. An occupation army, most of these troops were under-trained and out of shape. As he held on to Pusan, MacArthur's forces became more and more fit. The intense heat of summer was also a problem, and American morale was extremely low during this period. The worst was seen in "bug-out fever", where US troops would flee battle, throwing down weapons as they ran. The North Korean troops were battle-hardened veterans by comparison, used to the terrain, formidable fighters, and highly mobile. Once more, in the comparison of North Korean quick-strike capabilities and firm resolve versus an under-motivated and slow to react American army, this early phase of the Korean War foreshadowed the Vietnam War. Also, as in Vietnam, strategic bombing, which had played such a vital part in World War II, never worked very well against North Korea, which simply wasn't industrialized enough for bombing to have a devastating impact.