Post-1945 developments in China and Korea
(i) Post-1945 developments in China and Korea led to the intensification of the Cold War. In China, the Communists gained power in 1949 under Mao Tse-Tung and People's Republic of China was established.
(ii) The United States refused to recognise the People's Republic of China, which was also denied entry into the United Nations; only Taiwan (Nationalist' China) was recognized.
(iii) The United States used its power of veto to keep communist China out of the U.N. and the Soviet Union efffectively boycotted the U.N. of this. However, this did not mean the establishment of friendly relations between the USSR and PRC: after 1950 their relations took a turn for the worse.
(iv) After the defeat of Japan in the World War II, Korea was divided into North Korea under Soviet control and South Korea under American control in accordance with the Potsdam Conference.
(v) South Korea was effectively a dictatorship with direct support from the USA. In North Korea a pro-Soviet Government was set-up. Neither the Soviet Union nor the U.S.A. recognised the governments which were opposed to them.
(vi) In 1950, North Korea invaded South Korea. The United Nations, whose permanent Security Council was dominated by capitalist states, declared North Korea the aggressor and set-up a unified UN command to repel the North Korean attack. General Mac Arthur of the USA I was named its commander. The UN troops pushed North Korean forces out of South Korea and entered deep into the North Korean territory, reaching the Chinese border. China then joined the North Korean troops to push the UN troops into South Korea. Ultimately an armistice was signed in 1953 bringing to an end the threat of an open war.
(vii) The Korean crisis was the first military struggle of the Cold War. The USA and USSR and PRC did not engage in much direct combat with one another (although North Korean aircrafts were actually flown by Soviet pilots) but they fought each others' client powers (the Republic of Korea and the Democratic Republic of Korea: neither was actually a democracy).