"Supervillain has a non-aggression pact with a country with winters hard as fuck and then decides to invade the frozen-balls-country in winter anyway"
Do you screenwriters want us to believe this shit? Are you even trying?
they invaded in June hoping to get it done before the winter. It's just that the Russian weather doesn't fuck around. (also that the dumbfuck nazi leadership didn't consider halting the advance and reinforcing supply lines when the going got tough)