December 11, 1941. only hours after Germany declared war on the US
December 8, 1941, the day after the Japanese attacked Pearl Harbor
No
On December 7th, 1941 (a date which will live in infamy), the Empire of Japan bombed the US naval base at Pearl Harbor. This caused the US to declare war on Japan.
Unlike Vietnam & the US Civil War, which were undeclared wars; Germany & the US declared war upon each other on the same date, 11 December 1941. Germany in the morning, the US in the afternoon.
now
For the United States, only the US Congress has the power to declare war. That's explicit in the US consitution.
1776
Britain.
Congress
25th Jan
The US did not declare war on Germany. Germany declared war on the US shortly after the Japanese attack on Hawaii.