The Sino-Soviet border conflict was a seven-month undeclared military conflict between the Soviet Union and China at the height of the Sino-Soviet split in 1969. The most serious of these border clashes—which brought the two communist-ruled countries to the brink of war—occurred in March 1969 in the vicinity of Zhenbao Island on the Ussuri River, also known as Damanskii Island in Russia. Chinese historians most commonly refer to the conflict as the Zhenbao Island incident. The conflict was finally resolved with future border demarcations.
What made the Soviets angered was a Mao Zedong statement in July 1964, in a meeting with a Japanese socialist delegation, that:
"Tsarist Russia had stripped China of vast territories in Siberia and the Far East as far as Kamchatka. China still had not presented a bill for this list. "