- On December 7, 1941, the Imperial Japanese Navy launched a surprise attack on the U.S. naval base at Pearl Harbor in Hawaii.
- This resulted in the destruction of much of the U.S. Pacific Fleet and caused thousands of casualties.
Unrestricted Submarine Warfare:
- Germany's resumption of unrestricted submarine warfare (known as the "Second Happy Time") in the Atlantic Ocean, including attacks on U.S. merchant ships, angered Americans and violated previous agreements.
The Atlantic Charter:
- In August 1941, President Franklin D. Roosevelt and British Prime Minister Winston Churchill jointly issued the Atlantic Charter, declaring their common goals. One of these goals was "the right of peoples of every faith and every Nation to choose the form of government under which they will live."
- This was perceived as a challenge to authoritarian regimes like Nazi Germany and Japan.
Aid to Britain:
- Throughout 1941, the U.S. provided increasing economic and military support to Britain and its allies through programs like Lend-Lease. Britain was fighting against Germany by this time, so American aid indirectly involved the U.S. in the European conflict.
Sinking of U.S. Ships:
- Incidents occurred prior to Pearl Harbor where German U-Boats fired on and sank U.S. merchant ships carrying food or war supplies without prior warning, despite public assurances from Germany it would avoid direct conflicts of any nature with the United States.