Which nations were involved in the Nonaggression Pact of 1939?

The nonaggression pact of1939 was a treaty or agreement between the Soviet Union and Nazi Germany to not fight each other in WW2. The ideology of this was to delay a two front war for Germany as long as possible, unlike WW1. Hitler never intended to keep that promise though. It was just a delaying tactic, and a good one at that. Stalin never saw it coming.