What was the USSR doing between September 1939 and June 1941? It was allied with nazi Germany, of course. Historian Roger Moorhouse describes the lasting impact of the Molotov-Ribbentrop pact, and the strategic factors that ended it.
Roger Moorhouse
The Devils’ Alliance
Roger Moorhouse’s books: https://www.rogermoorhouse.com/books
Map: The division of eastern Europe according to the secret protocols of the pact
