New York World-Telegram, front page, December 8, 1941
The Pearl Harbor attack came as a profound shock to Americans and led directly to U.S. entry into World War II in both the Pacific and European theaters. News of the devastating attack ended the prewar isolationist‐interventionist divide in Congress and unified the country.
World War II: Declaring War on Japan
At 7:55 a.m. on December 7, 1941, Japanese naval and air forces launched a surprise attack on the U.S. naval base in Pearl Harbor, Hawaii, with devastating results. In less than two hours, Japanese bombers destroyed 19 American naval ships and more than 300 airplanes. A total of 2,403 Americans lost their lives; 1,178 others were wounded. Speaking before a joint session of Congress the next day, President Franklin D. Roosevelt requested a declaration of war on Japan. Congress approved the resolution in less than an hour.
That day ended isolationism for any realist.
Senator Arthur H. Vandenberg of Michigan, The Private Papers of Senator Vandenberg, 1941