Mao’s central concerns lay with asserting self-reliance and opposing the two superpowers, whom he argued tended to collude against China, even though their interests were fundamentally antagonistic. At the heart of their collusion, in his view, was their opposition to China’s acquisition of nuclear weapons. China’s first nuclear test took place in October 1964, and for a time it alarmed both the Soviet Union and the United States. Mao was so exercised by the threat of war from the north as well as from the east that he ordered, at tremendous cost, that a third front of defence and military related industries be developed in the mountainous redoubt of Sichuan, deep in the interior. However, the American intervention in Vietnam, which had been prompted initially by concerns to contain China and to disprove the effectiveness of Maoist revolutionary warfare, proved to be a turning point. The United States, seeking to limit the war to prevent a rerun of the Korean War, did not invade the north, but confined its ground fighting to the south and attacked the north only from the air and the sea. This meant that the Soviet Union, as well as China, was drawn in to coming to the defence of a fellow socialist country. But far from bringing the two communist giants together, the war divided them still further as Mao rejected the Soviet proposal for united action. Meanwhile, a tacit understanding was reached with the United States that its forces would not invade the north or attack China and that China would not directly enter the war. That understanding had been reached in part as a result of the Chinese demonstration of discrete commitment by helping to arm the North Vietnamese and by the visible, but unpublicized, deployment of Chinese troops in the north. Once convinced that there would not be repeat of Korea, Mao unleashed the Cultural Revolution, which was designed to sweep away his domestic Soviet-style ‘revisionist’ opponents and establish a new revolutionary political culture for the country. The spillover into foreign affairs was disastrous in the short term as it alienated many of the Asian countries that had previously been cultivated on geopolitical grounds, including Burma, Cambodia and North Korea.