What two major events led to the Soviet Unions involvement in World War 2?

Answer 1

Great Britian and France had approched the Soviet Union to become involved in a treaty to help contain Germany's expanionist policies prior to the beginning of WW2. Instead of joining in an alliance with these nations, Stalin, the leader of the USSR signed an agreement with Hitler called the German- Soviet Non- Aggression Pact. This was a pact of "friendship". One of the secret parts of this pact was this: Should Germany attack Poland, the USSR would take control of the eastern half of Poland. Thus, when the war began, the USSR had no interest in helping POland or anyone else. Their part of this deal was their half of Poland. On a military basis, the Poles were engaged with Germany on their western front. The USSR for the most part simply "walked" into Poland. For military purposes the Secret Police of the USSR executed 15,000 Polish military officers and other Polish troops in the USSR's half of Poland. (this was well known to the Poles, however, not officially revealed until KGB files were opened in the late 1980's.)

The USSR was forced into the war against Germany because in 1940 Germany broke the Non-Agression Pact with the USSR and invaded Russia.