The alliance with Soviet Russia was always one of convenience, and everyone realised it. They both needed it because they both hated Poland and wanted to dismember her. Later Hitler needed it to protect his rear while he dealt with the French, and Stalin needed it to buy time to rebuild the red army following the purges and the debacle in Finland. There was never any doubt that the two would be at war with one another. They were total idealogical opponents for a start off, and Hitlers grand plan was for “lebensraum” (living space) in the East. Inevitably that meant war with the Russians.