In 1994, Russian historian T. S. Bushuyeva found an archived version of the speech in the USSR Special Archives. I was unable to find any criticisms by mainstream historians since the authoritative document was discovered. Curiously, it seems as though American historians choose to just not discuss it.
Stalin's speech to a Politburo meeting on August 19, 1939:
The Russian historian Bushuyeva noted that while this document clearly confirms that Stalin had aggressive intentions, she cautiously added a quote by Clausewitz which essentially reminds that wars tend to a follow a path of their own, regardless of what is planned or said.The question of war or peace has entered a critical phase for us. If we conclude a mutual assistance pact with France and Great Britain, Germany will back off from Poland and seek a modus vivendi with the Western powers. War would be avoided, but down the road events could become dangerous for the USSR. If we accept Germany's proposal and conclude a non-aggression pact with her, she will of course invade Poland, and the intervention of France and England in that would be unavoidable. Western Europe would be subjected to serious upheavals and disorder. Under those conditions, we would have a great opportunity to stay out of the conflict, and we could plan the opportune time for us to enter the war.
The experience of the last 20 years has shown that in peacetime the Communist movement is never strong enough to seize power. The dictatorship of such a party will only become possible as the result of a major war.
Our choice is clear. We must accept the German proposal and politely send the Anglo-French mission home. Our immediate advantage will be to take Poland to the gates of Warsaw, as well as Ukrainian Galicia ...
For the realization of these plans it is essential that the war continue for a long as possible, and all forces, with which we are actively involved, should be directed toward this goal ...
Let us consider a second possibility, that is, a victory by Germany ... It is obvious that Germany will be too occupied elsewhere to turn against us. In a conquered France, the French Communist Party will be very strong. The Communist revolution will break out unavoidably, and we will be able to fully exploit this situation to come to the aid of France and make it our ally. In addition, all the nations that fall under the "protection" of a victorious Germany will also become our allies. This presents for us a broad field of action in which to develop the world revolution.
Comrades! It is in the interest of the USSR -- the workers' homeland -- that war breaks out between the Reich and the capitalist Anglo-French block. Everything should be done so that this drags out as long as possible with the goal of weakening both sides. For this reason, it is imperative that we agree to conclude the pact proposed by Germany, and then work that this war, which will one day be declared, is carried out after the greatest possible passage of time...
I have tried to "dig" other variations of this speech since it is translated, but this seems to be the only translation published.
