The Sino-Soviet split was the gradual worsening of relations between China and the Union of Soviet Socialist Republics (USSR) during the Cold War. This was primarily caused by divergences that arose from their different interpretations and practical applications of Marxism–Leninism, as influenced by their respective geopolitics during the Cold War of 1947–1991. 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 leader Mao Zedong decried as 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, China resented the Soviet Union's growing ties with India due to factors such as the Sino-Indian border dispute, while the Soviet Union feared that Mao was unconcerned about the drastic consequences of nuclear warfare.