After WWII Soviet forces occupied the Northern half of Korea and the United States occupied the southern half.  This was the start of the Korean War.  The Soviet decided to then invades South Korea, and since the Soviet was basically ignoring the U.N and boycotting it, they could not stop the U.N from putting troops in S. Korea.  The war then kept bouncing back between the U.S Army and the N. Korea Army.  In not to long N. Korea owned all of Korea.  After this China poured into the war because they wanted Korea.  The U.S forces then drove the U.N forces out enough and China captured South Korea.  This war was really a mess. The U.S. only aimed to push the North Koreans back beyond the 38th parallel, and finally accomplished it.  This war really showed the power of Communist China. 

After WWII the French decided to fight the independence of the colonies they had captures.  This is really what started the Vietnam War.  At the peace conference in Geneva, the U.S. tried to limit the communist influence in Vietnam.  Communists gained power in S. Vietnam.  North Vietnamese attacked two U.S. destroyers in the Gulf of Tonkin.  This caused the U.S to attack in Vietnam now.  The U.S had the most firepower and technology in the way but it was hard to fight the guerilla tactics by the Vietnamese.  Finally North Vietnamese invaded South Vietnam and within six weeks had gained control of all of Vietnam