Sino-Soviet split: Russia and the People's Republic of China agree to de-target their nuclear weapons against each other.
The Sino-Soviet split was the breaking of political relations between the People's Republic of China and the Soviet Union caused by doctrinal divergences that arose from their different interpretations and practical applications of Marxism–Leninism, as influenced by their respective geopolitics during the Cold War of 1945–1991. In the late 1950s and early 1960s, Sino-Soviet debates about the interpretation of orthodox Marxism became specific disputes about the Soviet Union's policies of national de-Stalinization and international peaceful coexistence with the Western Bloc, which Chinese founding father Mao Zedong decried as Marxist revisionism. Against that ideological background, China took a belligerent stance towards the Western world, and publicly rejected the Soviet Union's policy of peaceful coexistence between the Western Bloc and Eastern Bloc. In addition, Beijing resented the Soviet Union's growing ties with India due to factors such as the Sino-Indian border dispute, and Moscow feared that Mao was too nonchalant about the horrors of nuclear warfare.
In 1956, CPSU first secretary Nikita Khrushchev denounced Stalin and Stalinism in the speech On the Cult of Personality and its Consequences and began the de-Stalinization of the USSR. Mao and the Chinese leadership were appalled as the PRC and the USSR progressively diverged in their interpretations and applications of Leninist theory. By 1961, their intractable ideological differences provoked the PRC's formal denunciation of Soviet communism as the work of "revisionist traitors" in the USSR. The PRC also declared the Soviet Union social imperialist. For Eastern Bloc countries, the Sino-Soviet split was a question of who would lead the revolution for world communism, and to whom (China or the USSR) the vanguard parties of the world would turn for political advice, financial aid, and military assistance. In that vein, both countries competed for the leadership of world communism through the vanguard parties native to the countries in their spheres of influence.In the Western world, the Sino-Soviet split transformed the bi-polar cold war into a tri-polar one. The rivalry facilitated Mao's realization of Sino-American rapprochement with the US President Richard Nixon's visit to China in 1972. In the West, the policies of Triangular Diplomacy and linkage policy emerged. Moreover, the occurrence of the Sino-Soviet split also voided the concept of Monolithic Communism, the Western perception that the communist nations were collectively a unitary actor in post–Second World War geopolitics, especially during the 1947–1950 period in the Vietnam War, when the US intervened to the First Indochina War (1946–1954). However, the USSR and China continued to cooperate in Northern Vietnam into the 1970s, despite rivalry elsewhere. Historically, the Sino-Soviet split facilitated the Marxist–Leninist Realpolitik with which Mao established the tri-polar geopolitics (PRC–USA–USSR) of the late-period Cold War (1956–1991) to create an anti-Soviet front, which Maoists connected to Three Worlds Theory. According to Lüthi, there is "no documentary evidence that the Chinese or the Soviets thought about their relationship within a triangular framework during the period." The period has been compared to nominally quad-polar geopolitics (PRC-UK-USA-USSR) until the Suez Crisis of 1956.