Why did U.S.S.R enter world war 2?

Answer 1

The Soviet Union knew the German Nazis would invade their nation to get their raw materials, oil and land. They signed a non-aggression pact with Germany hoping to buy time and build up their forces. Then German Nazis did invade Russia and the USSR was forced into the war.

Answer 2

Germany's attack code named Barbarossa on the Soviet Union required no

less then placing it in a state of war.