It's not.
Communism is a type of an economy. The UN does not have a government or an economy. It is a body where representatives of nations meet. Some of those countries are communist (fewer an fewer).
No. China is officially communist, as are Laos and Vietnam (although one would debate how truly communist these are). North Korea is not officially communist, but in every other respect, it is.
The Northern Communist part of Vietnam came out victorious, they declared Independance and even to this day they could still be partly Communist
UN forces pushed the Communist back from Pusan.............and advanced north
North Korea was and remains a communist nation, and in 1950 it invaded the non-communist nation of South Korea. The UN acted to defeat the invasion. South Korea as a result did not become communist.
To witch hunt for Communist sympathizers.
to investigate communist activity within America
Karl Marx became famous by starting communism. Partly by writing the theory ('Das Kapital') and by building an Internal communist movement.
being communist sympathers
North Korea has been a communist nation for decades. The current head of state is the dictator Kim Jong-un. North Korea and Cuba are odd communist regimes. This is because in the past, it was rare that in a communist state, other leading communists have not taken to having the reins of government be passed down among family members. In Cuba we have the Castro brothers, and in North Korea Jong-un's father was the previous communist dictator. Most Marxists have no tolerance for "monarchy" style leaderships.
Walt Disney.
HUAC, the House Un-American Activities Committee
China wasn’t kept out. They are one of the 3 major countries in the UN.