On December 7, 1941, Imperial Japanese forces launched a surprise attack on the US naval base at Pearl Harbor in Hawaii. This attack, which resulted in the deaths of over 2,400 Americans and the destruction of much of the US Pacific Fleet, prompted the United States to declare war on Japan the following day.
2. Germany and Italy's declaration of war on the United States:
In response to the United States' declaration of war on Japan, Germany and Italy, which were allied with Japan as part of the Axis Powers, declared war on the United States on December 11, 1941. This action officially brought the United States into World War II.
3. Unrestricted submarine warfare:
Prior to the United States' entry into World War II, Germany had been waging an unrestricted submarine warfare campaign against Allied shipping in the Atlantic Ocean. This campaign, which resulted in the sinking of numerous merchant ships and the deaths of thousands of civilians, was a major factor in the United States' decision to join the war.
4. The lend-lease program:
In the lead-up to World War II, the United States had been providing military aid to Britain and its allies through the lend-lease program. This program, which allowed Britain and other countries to purchase American war materials on credit, was a significant factor in helping the Allies to resist Germany's aggression.
5. Roosevelt's "Four Freedoms" speech:
In his 1941 State of the Union address, President Franklin D. Roosevelt outlined four essential freedoms that he believed should be guaranteed to all people: freedom of speech, freedom of worship, freedom from want, and freedom from fear. This speech, which resonated with Americans and people around the world, helped to rally support for the United States' entry into World War II.