<P> After 1946, the CCP was increasingly successful in the Civil War . On October 1, 1949, the People's Republic of China was proclaimed by Mao Zedong, and by May 1950 the KMT had been expelled from Mainland China, remaining in control of Taiwan . With the creation of the People's Republic of China, the supreme political authority in the two countries became centred in two communist parties, both espousing revolutionary, Marxist--Leninist ideology: the Communist Party of China and the Communist Party of the Soviet Union . </P> <P> After the establishment of the People's Republic of China, a sensitive issue which influenced the Sino - Soviet relationship emerged . As a condition of fighting the Kwantung Army at the end of the Second World War, the Soviet Union received usage rights of the China Far East Railway, the South Manchuria Railway, Lushun (also known as Port Arthur) and Dalian . These privileges were significant in the Asian strategies of the Soviet Union because Port Arthur and Dalian were ice - free ports for the Soviet Navy, and the China Far East Railway and the South Manchuria Railway were the essential arterial communications which connected Siberia to Port Arthur and Dalian . As Mao Zedong thought that the usage rights of the Chinese Eastern Railway, the South Manchuria Railway, the Port Arthur and Dalian were part of Chinese state sovereignty, he required the Soviet Union to return these interests to China, and this was a crucial part of the Sino - Soviet Treaty of Friendship . Joseph Stalin initially refused this treaty, but finally made a great concession, and agreed with this treaty under the various stresses of the period . </P> <P> Since the Sino - Soviet Treaty of Friendship resulted in the Soviet Union losing its naval bases in Port Arthur and Dalian, the issue that Stalin had to face was to find a new ice - free port as a Soviet naval base . This issue motivated Stalin's support for allowing Kim Il - Sung to launch the Korean War . However, both Kim Il - Sung and Stalin did not consider that the United States would intervene into that war immediately, if at all . Kim Il - Sung could not sustain the attack against the US Army . When Kim Il - Sung required military assistance from the Soviet Union and China, Mao agreed to send Chinese troops, but asked the Soviet Air Force to provide air cover . As the two leaders distrusted each other, Stalin agreed with sending Chinese troops to Korea, but refused to provide air cover . Since without the air cover from the Soviet Union, Mao once considered that China did not send troops into Korea, and Stalin at one time decided to give up the Korea Peninsula . After much cogitation, Mao solely sent Chinese troops into Korea on 19 October 1950 under an extremely hard Chinese economic and military situation . This activity ultimately changed the Sino - Soviet relationship . After 12 days of Chinese troops entering the war, Stalin allowed the Soviet Air Force to provide air cover, and supported more aid to China . Mao sending Chinese troops to take part in the Korean War was followed by large - scale economic and military cooperation between China and the Soviet Union, and the friendly relationship of the two countries changed from titular to virtual . In one less known example of the Sino - Soviet military cooperation, in April--June 1952 a group of Soviet Tupolev Tu - 4 aircraft were based in Beijing to perform reconnaissance missions on American fusion bomb tests in the Pacific . </P> <P> Thus, in the immediate years after the PRC was proclaimed, the Soviet Union became its closest ally . Soviet design, equipment and skilled labour was set out to help industrialize and modernize the PRC . But the extent of actual support, while not insignificant, fell well below Chinese expectations . In the 1960s, relations became deeply strained following the Sino - Soviet Split, culminating in the Sino - Soviet border conflict in 1969 . Increasingly, the PRC began to consider the Soviet Union, which it viewed as Social imperialist, as the greatest threat it faced . In turn, overtures were made between the PRC and the US, such as in the Ping Pong Diplomacy and the 1972 Nixon visit to China . </P>

When did relations between china and the soviet union begin to improve