World War II: U.S. president Franklin D. Roosevelt signed Executive Order 9066, authorizing the forcible relocation of over 112,000 Japanese Americans to internment camps.

World War II or the Second World War was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all of the world's countries participated, with many nations mobilising all resources in pursuit of total war. Tanks and aircraft played major roles, enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war. World War II is the deadliest conflict in history, causing the death of 70 to 85 million people, more than half of whom were civilians. Millions died in genocides, including the Holocaust, and by massacres, starvation, and disease. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were tried for war crimes.

Franklin Delano Roosevelt, also known as FDR, was the 32nd president of the United States from 1933 until his death in 1945. He is the longest-serving U.S. president, and the only one to have served more than two terms. His first two terms were centered on combating the Great Depression, while his third and fourth saw him shift his focus to America's involvement in World War II.

Executive Order 9066 was a United States presidential executive order signed and issued during World War II by United States president Franklin D. Roosevelt on February 19, 1942. "This order authorized the forced removal of all persons deemed a threat to national security from the West Coast to 'relocation centers' further inland—resulting in the incarceration of Japanese Americans." Two-thirds of the 125,000 people displaced were U.S. citizens.

During World War II, the United States forcibly relocated and incarcerated about 120,000 people of Japanese descent in ten concentration camps operated by the War Relocation Authority (WRA), mostly in the western interior of the country. About two-thirds were U.S. citizens. These actions were initiated by Executive Order 9066, issued by President Franklin D. Roosevelt on February 19, 1942, following Imperial Japan's attack on Pearl Harbor on December 7, 1941. About 127,000 Japanese Americans then lived in the continental U.S., of which about 112,000 lived on the West Coast. About 80,000 were Nisei and Sansei. The rest were Issei immigrants born in Japan, who were ineligible for citizenship. In Hawaii, where more than 150,000 Japanese Americans comprised more than one-third of the territory's population, only 1,200 to 1,800 were incarcerated.