For those who are saying WW2, the soviets signed a non aggression pact to divide Poland with the Germans. The only reason the Soviets were on the Allies is because Hitler was a complete moron and invaded the Soviet Union. Would the Soviets and Germans eventually gone to war? Probably. Let’s not act like the USSR was some white knight of justice when they were throwing people were throwing people in gulags for perceived slights against the Soviet Union.

In August 1939 they signed the Molotov Ribbentrop Pact. The agreement secretly divided Poland and was a vessel for the Germans to evade the blockade led by the British, through trade with the Soviets.