Why did the U.S enter World War II?

The United States entered World War II after being attacked by Japan at Pearl Harbor on December 7, 1941. The United States had no other realistic option after this attack occurred except to declare war on Japan.

There were several events that suggested the United States would eventually be involved in World War II. We had been openly helping Great Britain after the war began in Europe. We developed the Destroyers for Bases program where we gave Great Britain destroyers while Great Britain allowed us to build bases in British-controlled lands. We also created the Lend-Lease Act, which allowed us to lend or lease weapons to Great Britain if they would pay us after the war ended or if they returned the weapons to us. We created a hemispheric defense zone that allowed us to patrol the Atlantic Ocean. We then would inform the British where German submarines were located.

We also took actions that upset the Japanese. With the passage of the Export Control Act, we stopped selling Japan strategic materials they could use in war. This included scrap metal and oil. We also froze Japanese assets in our banks. The Japanese viewed the United States as their biggest threat to controlling the Pacific Ocean and lands in Asia. These actions upset Japan and led them to plan an attack on Pearl Harbor.

On December 7, 1941, Japan attacked the United States at Pearl Harbor, bringing us into the war.