On December 8th 1941 FDR gave his short "Day of Infamy" speech and Congress declared war on Japan. On December 9th Roosevelt outlined a more comprehensive view of the new war and reasons for the actions taken so far. The US was attacked on several fronts in the Pacific and FDR knew that conflict in Europe will follow suit against Germany and its allies. This is another perspective of the World War II Memorial in Washington DC. The flag is at half mast because I visited on September 11.
FDR's speech can be read here: http://docs.fdrlibrary.marist.edu/120941.HTML