Order 9066 granted the US military the power to declare any area it chose a “military area,” but the meaning and extent of this term are only vaguely indicated in the text. Although no ethnic or racial group is mentioned, it was for the most part Japanese Americans—two thirds of whom were born in the US and thus were American citizens—who were singled out when the order was put into effect. Those singled out, who numbered about 120,000, were rounded up and imprisoned without due process or any trial or formal accusation but simply on the basis of their race. About 2,000 German and Italian Americans were also interned as potential enemy agents after the passage of Order 9066.

In addition, Japanese Hawaiians were not incarcerated to the extent that Japanese Americans residing on the mainland US were. This is partly because, due to historical factors, Japanese Hawaiians—who constituted a larger proportion of the population in Hawaii than did Japanese Americans in the mainland—lived under more secure economic conditions with less overt racism, and were felt to be economically vital to the war effort.

At first, the evacuation was carried out on a voluntary basis, but when numbers of volunteers to relocate proved minimal, the military instituted forced removal.