IX.

The March North and China’s Entry

The U.S.-led forces might have reestablished the 38th parallel as the border between North and South Korea, ended the war, and declared that the Truman Doctrine’s policy of containing Communism had been achieved. Instead, MacArthur sent troops across the parallel into North Korea in early October. Historians later faulted MacArthur for taking this action without Truman’s approval, but evidence has since shown that Truman approved the march north at the end of August, even before the landing at Incheon. As the summer progressed, nearly all of Truman’s senior advisers decided the chance had come not only to contain Communism but to roll it back. Thus, National Security Council document 81 authorized MacArthur to 'roll back' the North Korean regime if there were no Soviet or Chinese threats to intervene. The document also instructed MacArthur to use only Korean troops near the Chinese border so as not to further antagonize China.

In September and October 1950 U.S. intelligence agencies generally concluded that China would not enter the war. On September 20 the Central Intelligence Agency (CIA) noted that there was a slight possibility that Chinese 'volunteers' might enter the fighting, and a month later it noted 'a number of reports' that units from Manchuria (along the Chinese border with Korea) might be sent to North Korea. Nonetheless, the CIA decided that 'the odds are that Communist China, like the USSR, will not openly intervene in North Korea.' MacArthur swept confidently onward. By October 19 UN troops had captured the North Korean capital, P’yŏngyang, lying 150 km (90 mi) northwest of the 38th parallel.

Three days earlier, Chinese troops had crossed their border at the Yalu River into North Korea. They dealt heavy losses to ROK troops and bloodied U.S. forces as well, then abruptly ceased offensives for three weeks. This incursion by China did not stop the American march to the Yalu. General Walter Bedell Smith, director of the CIA, wrote on November 1 that the Chinese 'probably genuinely fear an invasion of Manchuria.' He also predicted the Chinese would try to establish a buffer zone along the border for security 'regardless of the increased risk of general war.' However, the CIA still found insufficient evidence throughout November that China would mount a major offensive.

North Korean and Chinese documents released or declassified in the 1980s and 1990s tell a different story. China did not enter the war purely to protect its border. Rather, Mao decided early in the war that should the North Koreans falter, China had an obligation to help them because many North Koreans had sacrificed their lives alongside Chinese—in the Chinese revolution that overthrew the imperial government in 1911 to 1912, in resistance to Japan’s decades of occupation, and in the Chinese civil war of 1946 to 1949. On August 4, 1950, Mao told the Chinese Politburo (the highest decision-making body of the Chinese Communist Party) that he intended to send troops to Korea 'in the name of a volunteer army' should the Americans reverse the tide of battle. The day after UN troops crossed the 38th parallel, Mao informed Stalin of his decision to invade. In other words, it was not the approach of American troops on the Chinese border that prompted China’s attack; it was the American strategy to roll back North Korean Communism.

The North Koreans and Chinese apparently waited to attack UN forces until they were well inside North Korea in order to stretch the UN supply lines and gain time for a dramatic reversal on the battlefield. On November 24 MacArthur launched a general offensive all along the northern front, which was nearing the Yalu. He described it as a 'massive compression and envelopment,' a pincer movement to trap the remaining KPA forces that were backed into the mountainous northern part of the peninsula. The offensive rolled forward for three days against little or no resistance, with ROK units succeeding in entering the important city of Ch’ŏngjin on the upper east coast, 70 km (45 mi) short of China. Lost amid the victory were reports from U.S. reconnaissance pilots that long columns of enemy troops were 'swarming all over the countryside.'