In February 1942 FDR signed Executive Order 9066 authorizing the military to “prescribe military areas . . . from which any or all persons may be excluded… for protection against espionage and against sabotage to national-defense material, national-defense premises, and national-defense utilities.”
As a result of this order ~110,000 Americans of Japanese ancestry, two-thirds of them born in the USA, were sent to camps in desolate Western locations.
Although described as a precaution against espionage and sabotage, the implementation of this executive reflected strong anti-Japanese sentiments. In a 1943 report, Gen. John DeWitt, head of the Western Defense Command, stated that “racial characteristics” of Japanese Americans predisposed them to assist the invasion, and that it was “impossible” to distinguish loyal from disloyal Japanese American citizens, if there were any.