How much of western Europe did hilter control by the time the US joined?

Answer 1

Just about all of Western Europe was either under Hitler's direct control or influence by the time Germany declared war on the US, December 11, 1941.

In Scandinavia German troops occupied Norway and Denmark. Finland was a German ally, on the principal that my enemy's enemy is my friend. Stalin had just finished humiliating himself by picking a fight with the Finns and then performing so badly that some believe the poor Russian performance against the tiny Finnish army encouraged Hitler to go ahead and invade Russia. Sweden was officially neutral but definitely within the Nazi sphere of influence, and was the source of most Nazi iron ore, as well as crucial items such as machined parts and ball bearings.

German troops occupied Belgium and the Netherlands, as well as northern France. The rest of France, and all of France's overseas possessions and colonies, were under the control of the collaborationist Vichy regime, a Nazi puppet installed after Germany invaded and defeated France. Spain was under the control of Francisco Franco, a fascist dictator who won his civil war with help from Hitler and Mussolini. Portugal also had a fascist regime. Italy was under Mussolini, the original fascist but a definite junior partner in his alliance with Germany. Austria had been extinguished in 1938 and absorbed into greater Germany as the province of Ostmark. Czechoslovakia likewise lost its independence to Germany. Romania, Bulgaria and Hungary were German allies. Yugoslavia was conquered in two weeks in the summer of 1941. Greece was also occupied by the Nazis.

Only Switzerland remained officially neutral on mainland Europe, but even the Swiss had to allow free passage to German trains back and forth from Italy.