USCIS 128:106. Why did the United States enter World War II?

OpenAI. (2026). Why did the United States enter World War II?    [AI-generated infographic]. OpenAI.  Edited by Jennifer Gagliardi

 World War II began in 1939 in Europe. The war was fought between two major groups. The Allied Powers included England (Great Britain), France, and the Soviet Union (Russia). 

China also was a key Allied Power.  Soldiers from countries in the British Commonwealth, such as India and French colonies such as Algeria also supported the Allies.  

The Axis Powers included Germany, Italy, and Japan.

At first, the United States tried to stay out of the war. Many Americans remembered the losses of World War I and did not want to enter another war in Europe. However, the United States still supported the Allied Powers by sending supplies, food, weapons, and other aid.

During the early years of the war, Germany conquered many countries in Europe. Germany was led by Adolf Hitler and the Nazi Party. The Nazis believed in racist ideas and dictatorship.

During the war, Nazi Germany carried out the Holocaust, the mass murder of about six million Jewish people. Millions of other people were also persecuted and killed, including Roma people, disabled people, gay and lesbians, political prisoners, and others. Many people were imprisoned in concentration camps and death camps.

The most important reason the United States entered World War II was the Japanese attack on Pearl Harbor. On December 7, 1941, Japanese airplanes attacked the American naval base at Attack on Pearl Harbor in Hawaii.

The attack damaged or destroyed many ships and airplanes. More than 2,000 Americans were killed, and many others were injured. The attack shocked and angered the American people.

The next day, President Franklin D. Roosevelt asked Congress to declare war on Japan. Soon afterward, Germany and Italy declared war on the United States, and the United States officially entered World War II.

After Pearl Harbor, fear and racism against Japanese Americans increased in the United States. In 1942, President Roosevelt signed Executive Order 9066. This order led to the forced removal and incarceration of about 120,000 Japanese Americans.  About two-thirds of the people imprisoned were American citizens.

Even during this difficult time, many Japanese Americans served in the U.S. military. Units such as the 442nd Regimental Combat Team became famous for bravery during the war.

Years later, many Americans recognized that the incarceration was unjust. In 1988, the U.S. government officially apologized through the Civil Liberties Act of 1988 and provided payments to surviving former prisoners.

During World War II, the United States worked closely with Allied leaders such as Winston Churchill and Joseph Stalin. American factories produced military equipment, and millions of Americans served in the armed forces.

World War II ended in 1945 with the defeat of Germany, Italy, and Japan. After the war, many world leaders promised to protect human rights and prevent future genocides.

World War II changed the role of the United States in the world and made the country a major global power.