In 1941, Japan launched a surprise military strike on the U.S. Navy base at Pearl Harbor, Hawaii. The attack killed more than 2,400 Americans and thrust the U.S. into World War II (1939-1945). It also prompted another horror: the imprisonment of tens of thousands of American citizens on U.S. soil.

From 1942 to 1946, U.S. officials rounded up an estimated 120,000 people of Japanese descent—both American citizens and legal residents—and forced them to live in internment camps, including a temporary detention center in Arcadia, California (above).

The camps were formed under an executive order issued by President Franklin D. Roosevelt. At the time, many people feared that people of Japanese descent might turn against America and aid Japan if it were to invade.

Today, that imprisonment of Japanese Americans is widely condemned as one of the country’s darkest periods, fueled by racism and wartime paranoia. Earlier this year, lawmakers in California issued a formal apology to Japanese Americans for the state’s role in sending residents to internment camps. The U.S. government apologized in 1988, paying $20,000 in reparations to each victim.