Further proof that the Soviets bared much of the responsibility for the start of the war, right along with Germany.
In the mid-1930s both Mussolini and Stalin opposed Hitler's expansionism, and wanted to be part of the allies' efforts to contain him. But both were first discouraged by allied weakness and appeasement, and then won over to Hitler by promises of participation in Hitler's successes.
In the end, Stalin like Mussolini joined Hitler's gang of thugs, and by all reports remained loyal until, two years later, Hitler turned and invaded the Soviet Union.
Think of a gang of thugs in a bank heist: Mussolini is driving the car, Stalin is covering Hitler's back, Hitler is calling the shots, holding up the bank and shooting anyone resisting.