Security Council and Communism
Communists took power in most of China in 1949. The Americans would not allow the new communist government to join the Security Council. Instead the Chinese place on the Security Council remained occupied by the non-communist nationalists who, by 1949, only controlled the Chinese island of Taiwan.
The argument about who should represent China became another episode in the bitter Cold War. The Soviet Union demanded that the nationalist Chinese should leave the Security Council and give way to the communist Chinese. In protest, the Soviet representatives walked out of the Security Council in January 1950.
In June 1950 North Korea invaded South Korea and the Security Council met to discuss its response. The absence of representatives from the Soviet Union meant that they were not able to veto the American proposal to help South Korea.