Why was the Soviet Union expelled from the League of Nations in 1939?

The Soviet Union was kicked out of the League of Nations after they invaded Finland in November of 1939. The invasion was in clear violation of the principles of the League and represented exactly the kind of aggressive action that the League had been formed to prevent in the first place. The League of Nations had been notoriously weak and ineffectual in dealing with similar acts of aggression—such as Mussolini's invasion of Abyssinia and Hitler's occupation of Austria—in the past. The expulsion of the Soviet Union was one of the League's final acts as an organization. Ironically, in expelling the Soviets, the League was in breach of its own rules and regulations, as only seven out of fifteen members of its ruling Council voted for the expulsion.