Because of the new archives you can really get an insight into the day to day operation of an empire that combined the power and function of New York, Washington, LA, Detroit and SF into one centrally run from an office. Its a a baffling process where Stalin moves between editing movies, deciding how many tanks to build and what kind, who would lead what part of the local bureaucracy and how to respond to an inquiry from a major foreign state and those meeting might be on the same day.
I highly recommend Kotkin two volumes on Stalin!
Being interested in WW1-WW2 timeframe what always struck me is the difference between Hitler and Stalin based on their basic outlook.
Hitler world-view was basically pessimistic, all races were in a global struggle for dominance, and its either win now or lose everything for ever. Low chance of success, no matter, its not or never. Germans were simply not close to the largest ethnic group.
Stalin on the other hand was fundamentally a Communist. Being in the end successful was not really a question, the global revolution was coming and they would win. Its really only a question of how long it would take. History would inevitably push in their direction.
Stalin foreign policy (not unlike Chamberlains) was to pull Germany to his side, because his fundamental Geo-strategic believe was that the global communist revolution would happen when the Capitalist were fighting in war against each other. But this time, the 'right reactionaries' would find the Red Army supporting the revolutionary.
German attack on France/Britain was everything Stalin had dreamed about for 2 decades. Decades of work leading him to the promised land, the Great Capitalistic War. And his plan very well might have worked, it was a decent strategy. Germans invaded with tanks using Soviet fuel and many other materials. But, French Army and Nation were not as they were in WW1 and they collapsed like a house of cards within weeks. Germany had landed into total continental power and most nations of Eastern Europe preferred them to the Soviets.
Stalin plan turned from mopping up weak regimes into being opposed by major very aggressive continental power. The Blowback of this strategy was gigantic, with 50+ million Soviets dying until it was over.
I despise Stalin and all the Bolsheviks, but Russian history is endlessly fascinating.