Beginning in 1956, after Nikita Khrushchev denounced Stalin and Stalinism in the speech On the Cult of Personality and its Consequences (25 February 1956), the PRC and the USSR had progressively divergent interpretations of Marxist ideology; by 1961, their intractable differences of ideologic interpretation and praxis provoked the PRC's formal denunciation of Soviet communism as the work of "revisionist traitors" in the USSR. Among the Eastern bloc countries, the Sino-Soviet split was about who would lead the revolution for world communism, China or Russia, and to whom would the vanguard parties of the world turn for political advice, financial aid, and military assistance. In that vein, the USSR and the PRC competed for ideological leadership through the communist parties native to the countries in their spheres of influence. The Sino-Soviet split transformed the geopolitics of the bi-polar cold war into a tri-polar cold war, and facilitated Sino-American rapprochement and the 1972 Nixon visit to China. It ended the era of "monolithic communism. Historically, the ideological Sino-Soviet split facilitated the Marxist–Leninist Realpolitik by which Mao established the tri-polar geopolitics (PRC-USA-USSR) of the late-period Cold War. Historian Lorenz M. Lüthi said: The Sino–Soviet split was one of the key events of the Cold War, equal in importance to the construction of the Berlin Wall, the Cuban Missile Crisis, the Second Vietnam War, and Sino-American Rapprochement. The split helped to determine the framework of the second half of the Cold War in general, and influenced the course of the Second Vietnam War, in particular. Like a nasty divorce, it left bad memories and produced myths of innocence on both sides. Relations with Southeast Asian states The Soviet Union gradually became heavily involved in the contest for influence in Southeast Asia. Although the Soviet Union is usually associated with its diplomatic support for North Vietnam during the Vietnam War, it also played a significant role in other Southeast Asian countries. Prior to the rise of President Suharto, the Soviet Union's largest recipient of arms aid between 1958 and 1965 was Indonesia. The 1970s onwards + pp In the 1970s, the Soviet Union achieved rough nuclear parity with the United States, and surpassed it by the end of that decade with the deployment of the SS-18 missile. It perceived its own involvement as essential to the solution of any major international problem. Meanwhile, the Cold War gave way to Détente and a more complicated pattern