After World War II, why did the USSR want to control countries in Eastern Europe?

Answer: In USSR there was a very strong belief in the world Communist revolution. It was viewed as a historical law, i. e. inevitable. Moreover Eastern European Communist parties were controlled by USSR already before WW II.

Explanation: exportation of the revolution was one of the first things Communists thought about. They viewed themselves as pioneers freeing enslaved proletarian from the hands of bourgeoisie.