The Sino-Soviet split (1956-1966) was a time when the relations between the People's Republic of China and the Soviet Union weakened during the Cold War. Eventually, China's leader, Mao Zedong, decided to break the alliance with the Soviet Union.
The Soviet leader, Stalin, wanted to help spread communism in the world, including China. In the Second Sino-Japanese War, the Soviets gave weapons and supplies to the Kuomintang, and advised the Communists to ally with them against the Japanese Empire. The Chinese Civil War continued, however. After World War II, Stalin and the Soviet Union helped the Communists. Chinese leaders disliked the Soviet leaders for not helping Mao and the Communists from the start.
Suddenly, in 1953, Stalin died. Mao saw Stalin as the leader of Communism, but also had a bad relationship with the Soviet Union throughout his time as leader. The new Soviet leader, Nikita Khrushchev, was not like Stalin. He did not want capitalism to collapse like Stalin did. Mao got angry about this, and he wanted Nikita Khrushchev to help him fight the imperialists. Khrushchev said no, and then Mao decided that if Khrushchev was not going to cooperate, they would not work with each other anymore.
Later, there was peace between the USSR and China, but they were suspicious of each other. They were no longer allies, and Mao's supporters said that it had been a victory.