In 1951, two years after the communist victory over nationalists in the Chinese civil war, Beijing signed an agreement with Moscow -- accepting China's existing border with the USSR, as well as armed Soviet control over the Amur and the Ussuri rivers. The Cultural Revolution in China of the 1960s, essentially a power struggle between Mao and the government bureaucracy, created great internal instability. Beijing declared its border with the USSR was the result of "unequal" treaties made a century earlier. The Chinese nuclear detonation of 1964 brought angst to Kremlin. The Soviet invasion of Czechoslovakia in 1968 also increased Chinese suspicions of Moscow's intentions south of the Amur into Manchuria.
On March 2, 1969, a group of People's Liberation Army (PLA) troops ambushed Soviet border guards on Zhenbao Island. The Soviets suffered 59 dead, including a senior colonel, and 94 wounded. They retaliated on March 15 by bombarding Chinese troop concentrations on the Chinese bank of the Ussuri River and by storming Zhenbao Island. The Soviets sent four then-secret T-62 tanks to attack the Chinese patrols on the island from the other side of the river. One of the leading tanks was hit and the tank commander was killed. On March 16, 1969, the Soviets entered the island to collect their dead; the Chinese held their fire. On March 17, 1969, the Soviets tried to recover the disabled tank, but their effort was repelled by the Chinese artillery. On March 21, the Soviets sent a demolition team attempting to destroy the tank. The Chinese opened fire and thwarted the Soviets. With the help of divers of the Chinese navy, the PLA pulled the T-62 tank onshore.
In August, the PLA tried another provocation, this time near where we are, in Kazakhstan. A Chinese military patrol crossed into the Lake Zhalanashkol region, about 3 miles into the Kazakh SSR. The USSR was better prepared this time. the Soviet soldiers crossed the border to attack. The Soviets eliminated the Chinese patrol, crossed over into the Chinese border zone and killed about 30 Chinese soldiers. They continued to hold the Terekty River, an intermittent stream which flows China to Kazakhstan, till the Soviet Union dissolved in the 1990s.
After the Terekty incident, the USSR prepared contingency plans for Chinese reprisals. It was believed Chinese tank brigades would come rolling into Kazakhstan to threaten the vulnerable underbelly of the USSR at Almaty. The Charyn canyon was the first natural obstacle across the steppe, running north south along the border - if this line were held, the tanks would have to force their way through the far-easier-to-defend Dzungharian Gate to the north. We pass the machine gun pillboxes on the Kazakh side of Charyn, dotting the landscape, about 100m apart, all along the gorge.
During this time, US officials watched the ideological and political split between the Soviet Union and the People's Republic of China escalate into fighting on Sino-Soviet borders. Some U.S. officials wondered if the Soviet Union might launch attacks to take out Chinese nuclear weapons facilities.
The Sinologist Allen Whiting wrote to Henry Kissinger:
Between 1966 and 1969, Soviet military deployments doubled the number of ground force divisions near the Chinese border while bringing the units originally there from half to full strength. Soviet artillery, nuclear and conventional, is concentrated along China's northeast frontier with a firepower density estimated as comparable with that opposite NATO. Soviet 500-nautical mile nuclear missiles (SS-12) are deployed so as to threaten vital rail and industrial centers in Manchuria. During this period, existing Soviet airfields have been improved and additional bases constructed targetting China. Particularly salient for striking China's nuclear production facilities are ten new Russian airfields in Outer Mongolia.
Soviet military deployments and political behavior indicate an increasing probability of a Soviet attack on China, presumably aimed at destroying China's nuclear capability. A Sino-Soviet war raises the risk of nuclear weapons being used by one or both sides. A Soviet attack on China will increase the bitter hatred and siege mentality with which the Chinese are likely to view the world for the rest of this century.