Originally Posted by PzJgr

The kicker here is that both Great Britain and France pledged their support to Poland in an effort to deter Hitler from invading. Now in the scenario presented, the USSR is now in on the side of the Western Allies. So, with Hitler invading, the USSR would 'actually' be entering Poland to save their 'fellow' slavic comarades.

As for Italy. The only reason Mussolini entered the war was watching his Facist subordinate (Hitler) taking over most of Europe so he jumped in so as not to be left behind even though he knew Italy was not prepared for a long drawn out war. So,,,,,I do not believe he would have jumped in just yet with hitler taking on 3 countries. He would have pulled a Franco and sat this one out.