The Sino-Soviet border conflict, also known as the Sino-Soviet crisis, was a seven-month undeclared military conflict between the Soviet Union and China in 1969, following the Sino-Soviet split. The most serious border clash, which brought the world's two largest socialist states to the brink of war, occurred near Damansky (Zhenbao) Island on the Ussuri (Wusuli) River in Manchuria. Clashes also took place in Xinjiang.
In 1964, the Chinese revisited the matter of the Sino-Soviet border demarcated in the 19th century, originally imposed upon the Qing dynasty by the Russian Empire by way of unequal treaties. Negotiations broke down amid heightening tensions and both sides began dramatically increasing military presence along the border. Sino-Soviet relations worsened further following the Soviet invasion of Czechoslovakia in 1968. Border confrontations escalated in March 1969 when a group of People's Liberation Army troops engaged Soviet border guards on Zhenbao Island in Manchuria, resulting in considerable casualties on both sides. Further clashes occurred in August at Tielieketi in Xinjiang and raised the prospect of an all-out nuclear exchange. The crisis de-escalated after Soviet Premier Alexei Kosygin met with Chinese Premier Zhou Enlai in September, and a ceasefire was ordered with a return to the status quo ante bellum.
