The USSR never allied with the Germans, it was a non-aggression pact, made after the USSR failed to get Britain, France, or Poland to support them in invading Germany in response to Czechoslovakia. Instead Britain, France, and Poland signed the Munich Agreement, dividing Czechoslovakia between Germany and Poland.
To be clear, even after the invasion of Poland in 1940, the western powers intended to support Germany against the USSR, Britain even tried to send troops to support Germany’s ally, Finland in the winter war, after the invasion of Poland, and was only prevented when it ended too quickly.
The USSR never allied with the Germans, it was a non-aggression pact, made after the USSR failed to get Britain, France, or Poland to support them in invading Germany in response to Czechoslovakia. Instead Britain, France, and Poland signed the Munich Agreement, dividing Czechoslovakia between Germany and Poland.
To be clear, even after the invasion of Poland in 1940, the western powers intended to support Germany against the USSR, Britain even tried to send troops to support Germany’s ally, Finland in the winter war, after the invasion of Poland, and was only prevented when it ended too quickly.