Odd account in the excerpt.
As if Russia had not been involved in the war prior to the German invasion.
Almost as if the author is trying to hide the fact that as Hitler was invading Poland from the west in 1939, his ally Stalin was invading it from the east
Also Russia invaded Finland and the Baltic States and took Bessarabia from Romania. Britain considered aiding the Finns against Russia.
It certainly does seem like a really shallow outline of events.
VDH does say “After conquering all of Western Europe, Hitler’s Germany felt itself invincible. It saw the Soviet Union as weak and ripe for a double-cross.”
So he implies the existence of the Molotov-Ribbentrop Pact, of which I am absolutely certain he is aware. I am equally sure he is aware of the USSR’s part in the dismemberment of Poland.