USSR and Germany signed Nazi-Soviet Pact on 23 August 1939
Both countries agreed to not attack e/o
Privately agreed to divide Poland between them
Hitler and Stalin mistrusted e/o
The Pact was an (i) agreement of convenience and (ii) mutual benefits
Stalin thought Britain and French were too weak to stand up to Hitler
Stalin built up USSR's military capability incase Hitler invaded them with the build up of time
However, fighting a war in Europe would result in (a)(i) Germany's manpower and (ii) resources being stretched and their (b) fighting capabilities limited
Hitler hoped the pact would (a) give him authority to take over Poland and (b) persuade allies to turn a blind eye to his activities