Executive Order 9066

On February 19, 1942 the President of the United States issued Executive Order 9066 - the order that set in motion the process whereby 120,000 mostly US citizens of Japanese descent were interned in camps for the remainder of the Second World War. The majority of those interned were natural born US citizens. In addition a significant minority were resident aliens or naturalized citizens. Finally, a small minority were German-American and Italian-American. 

Following his arrest U.S. citizen Fred T. Korematsu challenged this order, and had his challenge go all the way to the U.S. Supreme Court. There, in the 1944 decision Korematsu v. United States, the Supreme Court, by a 6-3 decision, upheld the right of the Federal Government to relocate citizens in such a fashion during wartime. This decision, the executive order, and the internment remains today among the most controversial decisions made by the wartime US leadership. An example of what these orders looked like in practice can be found here.