Britain and France declared war on Germany 3rd September 1939.
Germany declared war on the United States 11 December 1941 at which point the US then declared war on Germany.
The first US forces didn't really start arriving in the European theater until January 1942. Not surprising considering the attack by the Japanese at Pearl. The war in Europe had been in progress for 2 1/2 years by this time.
Anyway, in answer to your question, I would guess it must be related to Pearl Harbour as the US wasn't at war with anyone up to that point in time.
RTR