Germany and the Soviets had agreed a boundary between the lands they both wanted to conquer

And France and Britain agreed to boundaries in Czechoslovakia. You wouldn’t call the Munich Agreement an alliance though.

They then exploited it when Operation Barbarossa commenced and continued pushing the soviets back. Finally, once that was done

Except the USSR ended up with the territory they had demanded at the start of the winter war, in response to Finland aligning with Nazi Germany. Finland’s willingness to switch sides was due to them seeing the writing on the wall.