I'm concerned that some otherwise well-informed people might not understand the various organs of the United Nation, specifically, Security Council. All member nations belong to the General Assembly; only 15 serve on the Security Council. http://www.un.org/en/sc/
The Security Council has 5 permanent members -- Russia (who took USSR's seat), France, UK, USA, and China -- plus 10 rotating members. Each of 5 permanent members has veto power and can really frustrate the council.
In 1950 the Soviets walked out in protest and missed the opportunity to stop the UN from supporting South Korea agains Chinese and Soviet backed North Korea.
Here's a quick explanation-->