On August 23, 1939 Hitler and Stalin signed a non-agression pact, called the Molotov-Ribbentrop Treaty. Secret protocols of the treaty defined the territorial spheres of influence Germany and Russia would have after a successful invasion of Poland. Hitler had been creating justifications and laying plans for such an invasion since April.
According to the agreement, Russia would have control over Latvia, Estonia, and Finland, while Germany would gain control over Lithuania and Danzig. Poland would be partitioned into three major areas. The Warthland area, bordering Germany would be annexed outright to the German Reich, and all non-German inhabitants expelled to the east. Over 77,000 square miles of eastern Polish lands, with a population of over thirteen million would become Russian territory. The central area would become a German protectorate, named the General Gouvernement, governed by a German civil authority.