On December 7, 1941, the United States Congress declared war ( Pub. L. 77–328, 55 Stat. 795) on the Empire of Japan in response to that country's surprise attack on Pearl Harbor the prior day.
The President's description of December 7, 1941 as "a date which will live in infamy" was borne out; the date very quickly became shorthand for the Pearl Harbor attack in much the same way that November 22, 1963 and September 11, 2001 became inextricably associated with the assassination of John F.