When and how did the Soviet Union enter World War II?
Russia entered World War II twice. The first time was when Germany invaded Poland in 1939. Russia invaded from the east at the same time and gobbled up east Poland. That was in accordance with the non-aggression pact it signed with Germany. Then it functioned as a “friend” of Germany. Russia re-entered the war a few years later as a result of “Operation Barbarosa” when Germany invaded it in an effort to gain control over Russian wheat and oil.
The Soivet Union was in WW2 from the beginning, having signed a secret treaty with the Nazis in 1939, promising to secrelty help the Nazis destroy Poland, then divide it up. Once this was done, and Germany was in a position to invade USSR, the Soviets switched sides, luckily for us, and won the war, practically for us.
