Background
Pre WWII Politics
After the end of WWI, and due to the now frail nature of the German Reich, the Treaty of Rapallo was signed between Soviet Russia and the Reich. While the two states viewed each others political ideologies as the pure incarnate of evil, they were united in their hatred of Poland. Border and ideological disputes created extreme tension among the three states, and the treaty (nicknamed the Alliance of Convenience) was viewed as a temporary measure to ensure that Polish forces would be squashed. By the end of the 1920s however, the dynamic of military might had shifted dramatically, and the Reich began to believe that Poland would be severely underequipped to fight of a war on one front, let alone two. Germany also found that the USSR's now reduced army would struggle significantly to hold off a Polish counterattack, and thus another treaty was signed promising Germany neutrality in the case of a Polish invasion, ensuring that Poland wouldn’t be able to receive support from their biggest and most powerful ally at the time - France. This alliance also sparked hope for renewed German-Russian alliances, as war with Russia was not something under consideration by German leadership(Alexander 2019)
Beginnings of new Beginnings
While the new leader of the Reich Adolf Hitler spoke of war and conquest, war against Soviet Russia still did not appear to be obvious. His desire for "military sovereignty" meant that their secret relationship was still beneficial, and in a military conference held in East Prussia, the then Russian chief of military was designated to be the commander-in-chief of any future anti-Polish wars. Despite this, sentiment within Hitler's political circles was mixed about Russians. While most agreed that the ideology was akin to evil itself, it became clear that avoiding direct conflict would be beneficial to Germany, at least until their military was further strengthened. However, in 1936, Hitler developed an aggressive 4-year plan to push Germany to the forefront of European military and economic might. This plan also served to prepare for war against the USSR, and to capture key territories to help accelerate German production. In addition, Hitler began working in secret with Axis allies to coordinate anti-Soviet policies through the Anti-Comintern pact in hopes of getting more strategic positioning in an invasion of the USSR. Hitler even offered Poland entry to the pact repeatedly in hopes of getting another strategic ally, but Poland continued to decline due to the fact that it would require territorial concessions- a choice that would fundamentally change the balance of the eastern front(Alexander 2019).
Deployment
Despite them declining joining a clear alliance, Poland still attempted maintained strong relationships with Germany and stood by their existing non-aggression pact. But behind the scenes, Hitler began rallying against Poland. He asserted that Poland no longer served as an adequate barrier between Germany and Russia, and thus had to be neutralized. Stalin began taking notice of Hitlers rampant political aggression and pressure, and thus signed a joint-defensive pact with several allied powers in the hope of spreading out Germany's fronts. Poland also realigned itself with the Allies as an invasion became clearer, completely restructuring Hitlers plans. Thus, Germany had to reconsider its Allies and position in the attack and thus signed the German-Soviet non-aggression pact. Despite the pact, Hitler still stressed the importance of an eventual invasion of the USSR to gain strategic production points. Once Germany declared war on Poland and was met by declarations against themselves by Britain and France, it forced Hitler to become even closer to Stalin than he had ever hoped. Even with the Soviet invasion of Poland from the east, the Allies refused to declare war on the USSR further narrowing Hitlers options. Despite this, Hitler continued to assert that these treaties were temporary, and that long term peace or neutrality from the Soviet Union was impossible. Stability of the peace treaty was under severe scrutiny, as Soviet Russia began significant westward expansion towards the Baltic states creating conflicting territorial interests between the two powers (despite the fact that terms of the treaty allotted these territories to the USSR). Additionally, the failed invasion of Finland by the USSR appeared to have proved military weakness giving further reason for abandoning the treaty. Pressure increased from Axis allies and military leaders within the Reich to "stop concessions of the Reich's values" through their acceptance of Soviet neutrality, and thus Hitler decided to begin plans for the all-out invasion of the USSR - Operation Barbarossa(Nik 2016).