While most Americans expected the U.S. to enter the war, presumably in Europe or the Philippines, the nation was shocked to hear of Japan’s attack on Pearl Harbor on December 7, 1941. In the wake of the bombing, the West Coast appeared particularly vulnerable to another Japanese military offensive. A large population of Japanese Americans inhabited the western states and American military analysts feared some would conduct acts of sabotage on west-coast defense and agricultural industries.

Official relations between the governments of Japan and the United States had soured in the 1930s when Japan began its military conquest of Chinese territory. China, weakened by a civil war between nationalists and communists, represented an important strategic relationship for both the U.S. and Japan. Japan desperately needed China’s raw materials in order to continue its program of modernization. The U.S. needed a democratic Chinese government to counter both Japanese military expansion in the Pacific and the spread of communism in Asia. Liberal Japanese resented American anti-Japanese policies, particularly in California, where exclusionary laws were passed to prevent Japanese Americans from competing with U.S. citizens in the agricultural industry. In spite of these tensions, a 1941 federal report requested by Roosevelt indicated that more than 90 percent of Japanese Americans were considered loyal citizens. Nevertheless, under increasing pressure from agricultural associations, military advisors and influential California politicians, Roosevelt agreed to begin the necessary steps for possible internment of the Japanese-American population.

Ostensibly issued in the interest of national security, Proclamation No. 2537 permitted the arrest, detention and internment of enemy aliens who violated restricted areas, such as ports, water treatment plants or even areas prone to brush fires, for the duration of the war. A month later, a reluctant but resigned Roosevelt signed the War Department’s blanket Executive Order 9066, which authorized the physical removal of all Japanese Americans into internment camps.