Story highlights We must acknowledge the way a climate of fear enabled the US government to incarcerate its own citizens

Germans, Italians were arrested after Pearl Harbor, but Americans' fear of "persons of Japanese ancestry" was worst

Daniel Greene is adjunct professor of history at Northwestern University. The opinions in this article belong to the author

Yet America's unity was matched by its profound fears about national security in the days after Pearl Harbor. Well before December 7, 1941, Americans believed that enemy spies and saboteurs lived among us. Some did, though not nearly as many as we imagined. In 1940, the FBI reportedly received 3,000 complaints or tips every day regarding acts against America's national defense.

Daniel Greene

Amid this climate of fear, FBI Director J. Edgar Hoover ordered the Immigration and Naturalization Service to detain and question thousands suspected of having ties to America's enemies. Many Germans and Italians were arrested in the days after Pearl Harbor, but the American people's fear of "persons of Japanese ancestry" hardened the most.

In the months after the attack, the US government acted decisively on these fears, physically relocating more than 110,000 people of Japanese ancestry , more than two-thirds of whom were American citizens, to 10 inland camps across Arkansas, Arizona, California, Colorado, Utah, Idaho, and Wyoming. Many more temporary detention centers and assembly centers dotted the American landscape in 1942.

Although administered by an agency called the War Relocation Authority -- and referred to by the government as "relocation centers" -- these were American concentration camps.

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