The Nazis and Soviets were never really friends. First off, I wonder how much resentment some in Russia had as to the steep cost of exiting the WW1, maybe Loppar knows a bit.
Hitler totally hated the Soviets and knew for a long time before that he wanted to slam them and enslave them. It was just a matter of priorities.
He knew that as soon as he took Poland, there would be a war off to the west with Britain and France. they were in a state of poor military preparedness, and he could’t be concerned too much with anything the Soviets might do while the Nazis were dealing with that. He also knew the Soviets were likely to get nasty at some point in time, and they too had their military in only so good a state of preparedness.
So the Pact of Steel was dreamed up. In I think 1938, Hitler had Joachim von Ribbentrop, the German foreign minister, send out feelers to the Soviets. Vyacheslav Molotov, the Soviet foreign minister, was the man with whom I think a lot of the negotiations went through.
The idea was this: Look, we know we both hate each other, but I think we both know we both want to expand into the rest of Europe at about the same time, so why don’t we draw up a gentlemen’s agreement such that we get this, you get that, and we don’t bump elbows doing it.
The Germans would get the western 2/3 of Poland, and western Europe. the soviets would get the other 1/3 of Poland, Latvia, Lithuania, and Estonia. they would also get to invade Finland for more salt water access on the Baltic sea for naval strength.
The Soviets went for it hook, line and sinker, although I think Molotov did express some misgivings that likely save his life.
Hitler slammed the Poles, and after the Phony war went after the west, with the comfort of knowing the Soviets weren’t going to fuck with him while doing it. In June of 1941, Hitler still hadn’t taken out the British, but knew time was ticking on his opportunity to absolutely slam the Soviet Union while they would still be at a disadvantage of ignorance.
Maybe someone else can elaborate on the alliance with Hungary, Romania and Bulgaria. My understandilng is that Hitler said, “look, over to the east is this big, bad Soviet Union that wants to meddle in your internal affairs and might some day lean on your borders. Join forces with us and we will remove the threat and you get a slice of the spoils of battle.”