At the beginning of WWII, USSR Premier Josef Stalin and German dictator Adolf Hitler signed a non-aggression pact that also secretly agreed to divide eastern Europe between them. What changed it?
A) Stalin changed his mind and voided the pact
B) Hitler invaded the Soviet Union (USSR) (Battle of Stalingrad)
C) Poland joined the Ukraine in defeating both Germany and the USSR, stopping them
D) Britain attacked the USSR & Germany