From The Coldest Winter: America and the Korean War, by David Halberstam (Hyperion, 2007), pp. 337-339:
In late September, after the In Min Gun started a panicky retreat north, the Chinese began to edge ever closer to intervention. What they would do next—entering the war, taking terrible casualties, but stalemating the Americans and the United Nations in the process—they did for their own reasons, not out of any great love for the North Koreans. Their respect for the Koreans and Kim at that moment was in fact quite marginal. They felt the Koreans had gotten their country too easily: the Chinese, after all, had won their great victory by fighting a numerically and technologically superior foe for decades. In addition, Mao and the others were still irritated by the arrogance and brashness of Kim Il Sung.
The Chinese leaders had been appalled by Kim’s lack of response to their warnings about a possible amphibious landing at Inchon. Any Chinese commander who had disregarded such powerful, hard intelligence would have been relieved of command. In early August, as Chinese Army forces began to build up north of the Yalu, the Chinese sent one of their senior corps commanders, Deng Hua, to visit with his Korean military counterparts. Deng crossed the Yalu, got to the border town of Andong, and discovered that that was as far as he could go. The Koreans were not going to let him anywhere near the battle zone.
The Chinese decided to send their troops to Korea because Mao believed it was good for the new China and necessary for the future of the revolution, both domestically and internationally. He also feared what a failure to intervene would mean—that his China, for all its rhetoric, was not that different from the old China, a powerless giant when facing what was in their eyes the armies of Western oppressors. Therefore, almost from the moment it became clear that Kim’s offensive was doomed, Mao had begun the planning that would end with the use of Chinese troops in Korea. In early July, a time when Kim’s armies were still gaining singular successes on the battlefield, Mao had nonetheless ordered the creation of what became the Northeast Border Defense Army, the NEBDA, to be positioned along the Korean border. It was to include more than three armies from the Fourth Field Army, which had some of China’s best troops. Eventually the force numbered thirty-six divisions, or roughly (with support units) some seven hundred thousand troops. Seven artillery divisions and some antiaircraft units were eventually attached.
Mao had felt that there was a certain inevitability in China being pulled into the war, and he wanted to be as realistic as possible in gauging the price China would pay. On August 31, Zhou Enlai chaired a meeting on force levels where the senior people spoke not only of what they would need, but what it might cost in terms of potential casualties in the first year of a war with the Americans. The answer, they decided, was around 60,000 deaths and 140,000 wounded.
The Chinese decisions in the weeks following Inchon were essentially those of one man, Mao Zedong. He was the classic example of the revolutionary as true believer. Starting out with so little, he had been unusually successful during those long years of the civil war—and most of his judgments, however bloody and difficult, had turned out right. He was sure he understood the ordinary Chinese—the peasants—better than anyone else. He believed in China’s right to be a great nation again; that the source of its strength was his revolution; and that the revolution had succeeded because it had evoked the purity of the Chinese peasantry and so turned historic political suffering into military strength. His men had been better soldiers than their well-armed Nationalist opponents because of their beliefs. As the principal architect of the new China, in his mind he now charged himself with keeping the revolution true to itself. That kind of belief in a single strand of history and in yourself as its principal figure—in effect serving as history’s man—is powerful stuff; it has both its strengths and its weaknesses.
What Mao knew—about China’s peasants and their suffering, and the cruelty of the old order—he knew brilliantly; what he didn’t know, he didn’t know at all and often was unable to learn. That kind of success has the capacity to produce a terrible kind of megalomania. Epic revolutions probably demand someone with a supreme, invincible sense of self, a belief in the price that other men have to pay for the good of their vision; it was what allowed men like Mao and Stalin to rationalize great suffering for the good of the cause. But in such men there were no boundaries, no restraints, and what began as an all- consuming vision became almost inevitably a great nightmare as well; in time, monstrous crimes would be inflicted not on China’s foreign enemies, or even its domestic dissidents, but on its own loyal citizens, including many of the men who had served Mao so loyally in those years of civil war and then in Korea. But to understand Mao’s action at this critical juncture it is important to think of him always not just as the architect of a revolution but as its guardian as well, someone who believed that his enemies—of whom there were many, domestic and foreign—were always out to destroy his revolution and that he had to move against them before they moved against him.