The People’s Liberation Army Air Force established plans to fight against the United States Air Force, as well as plans to counter-attacks United States war planes near the southern Chinese border area.[12] China was obviously very sensitive to any possible United States attack from the air. Zhou Enlai asked visiting foreign diplomats to send a message to the United States: “If the United States launches a full-scale air attack on China, it would be the beginning of a war. A war has no limit.”[13] On April 12, Chinese Communist Party Central Committee’s Politburo held an extended meeting. The meeting discussed and passed The Resolution on Enhancing Defense Tasks, which stated that the United States escalation of the Vietnam War had “serious threatened” China’s nation security. “China will be prepared to put off the battle flames that the American imperialists will push to China,” “China will be fully prepared to counter enemy’s air attacks,” and “China will be prepared to fight a war on the small scale, medium scale, as well as on the large scale,” the document said.[14]

While China readied itself for a war against the United States, Chinese leaders also tried to express China’s grave concerns of the United States’s escalation of the war in Vietnam through diplomatic channels. China wanted to make its bottom line clear in order to avoid any misunderstanding that could lead to direct military conflicts with the United States. On April 2, Zhou Enlai took the opportunity of a visit to Pakistan, explaining three points that China held to Pakistani President Ayub Khan, who was about to visit the United States: “1. China will not initiate a war against the United States without provocation. 2. The words of Chinese people count. 3. China is prepared.” He also clearly defined what would constitute a war waged by the United States against China-if the United States limited attacks against China to air raids, it would be considered the beginning of a war.[15] Because Ayub Khan delayed his visit to the United States, Zhou Enlai took another opportunity during his visit to Tanzania and asked the President of Tanzania to rely China’s message to the United States.[16] On August 20, Zhou Enlai repeated China’s above policy to an official delegation from Zambia.[17]

An important measure China took to safeguard China’s national security was to put all possible efforts into support Vietnam’s resistance fight against the American invasion. Looking at recent history, China would never allow a situation in which a hostile super power takes actions of force in an area so closely bordering China, not to mention that the very act of escalating the war in Vietnam was considered hostile actions aimed at China. After the “Token Gulf Incident” took place, North Vietnamese leaders informed Chinese leaders that they planned to act cautiously and planned to try negotiations with the United States in order to prevent a direct attack by the United States on North Vietnam. It was highly possible that based on similar thinking, Chinese leaders agreed with North Vietnam’s precautionary plans, including plans of an attempt at peaceful negotiations.[18]

Starting the spring of 1965, because the United States increased air attacks on North Vietnam and also sent ground troops to participate in the Vietnam War directly, Chinese leaders began to oppose Vietnam’s position in peaceful negotiations with the United States. In early April, the first secretary of the Vietnam Minh party, Le Duan, visited China and requested China to send supporting troops to North Vietnam. The two sides signed a series of agreements concerning Chinese military assistance and economic aid to North Vietnam. Toward the end of May, a delegation of Vietnam military officials visited China to discuss specific arrangements for Chinese assistance and coordination of war strategies. Beginning in June of 1965, Chinese People’s Liberation Army’s supporting troops entered Vietnam, participating in anti-air battles, the construction of military facilities, railways, and providing auxiliary supports. By July of 1970, China successively sent 320,000 anti-air defense, railway, construction and auxiliary troops to Vietnam, with as many as 170,000 troops in a single year.[19]

Clearly, after losing support provided by the China-Soviet Union alliance, China’s abilities to counter United States attacks, especially the abilities to coordinate air power with naval power, were severely weakened. Therefore, the threats posed on China’s national security by an escalating Vietnam War, as well as United States invasions of Chinese air and sea territories, also increased. China had no choice but to take strong emergency counter measures. This outcome undoubtedly increased the possibility of direct military confrontations between China and the United States.

During the same period, the worsening of China’s security environment was also exhibited in the continuous border disputes with the Soviet Union. China and the Soviet Union shared the longest inland borders in the world at that time. Territorial and border disputes had existed for a long time between China and the Soviet Union prior to the border clashes in the 1960s. The situation was created by complex historical and current events. After the founding of the People’s Republic of China, in order to maintain a Soviet Union-China alliance in the overall strategic environment, and considering the historical aspects of the border disputes, China was prepared to agree to base the entire border between China and the Soviet Union on the many unequal treaties left from various periods of history. After the bilateral relationship deteriorated, both sides started paying attention to border issues. Both sides increased forces along the borders and started to accuse each other of initiating conflicts along the borders. From the viewpoint of historical development, border disputes have indeed become an indicator of increased hostility between China and the Soviet Union, as well as a tool used by both sides to resolve mutual conflicts. Especially for the Soviet Union, border disputes become a method of placing political and military pressure on China.

From the first incident of the border clashes took place in China’s Xing Jiang province in August of 1960s, there had been no peaceful days along the Soviet-Chinese borders. According to statistics published by the Chinese side, from August of 1960 to October of 1964, there were more than 1,000 border disputes.[20] During that time, not only did the Soviet Union create military conflicts along the borders, Soviet leaders also used China’s territory disputes with other countries, especially those with India, to attack China’s foreign policy and to damage China’s international reputation.[21] In response to these Soviet attacks, The People’s Daily published an editorial titled on The Declaration of the American Communist Party on March 8 in 1963. For the first time, the editorial openly mentioned the unequal treaties regarding Chinese and Russian territories. The article raised a sharp question to the Soviet Union: “If the Soviet Union is now keen in bringing up the issues of unequal treaties [China had with other countries] in history, does the Soviet Union want to discuss all of the unequal treaties?”[22]