[dude with glasses in a communist t-shirt, arguing] I’m the only leftist here, your opinions are TRASH
[dude holding a theory book on smug, arguing] Read theory you losers, you’re all WRONG
[dude in an anarchist hoodie, arguing] Nuh-uh, I’m the only leftist here, you’re SHITLIBS
[the three dudes are now caught in a cartoon fight, glasses gone flying, punches everywhere, while a firing squad of nazis are targeting them with rifles]
[a confused nazi asks] Why… why are they still arguing?
No, because there was never an agreement about partitioning. It was about spheres of influence, which Nazi Germany broke, and further the USSR entered Poland weeks after the Nazis invaded in order to prevent the entirety of Poland from falling to the Nazis, largely sticking to areas only a few decades prior Poland had invaded and annexed.
There’s also no evidence the Soviets didn’t expect the Nazis to invade. They didn’t get the timeframe right, but they expected it the entire time. And no, the Soviets weren’t imperialist.