FDR was very much a racist who was going along with a plot concocted by a wealthy group of agricultural interests to dispossess Japanese-American citizens and immigrants of their farmlands, under the pretense of national security:
> Only hours after the Pearl Harbor attack on Dec. 7. 1941, Austin E. Anson, managing secretary of California's powerful Salinas Valley Vegetable Grower-Shipper Association, was dispatched to Washington to urge federal authorities to remove all individuals of Japanese ancestry from the West Coast. In an interview for the May 1942 Saturday Evening Post, Anson told how he drew a frightful scenario for the War and Navy departments, the attorney general and every congressman he could get to listen to him: an invading army coming ashore in Monterey Bay and advancing into the Salinas Valley while Japanese residents blew up bridges, disrupting traffic and sabotaging local defenses.
> By the end of the war, according to the U.S. Department of Agriculture, "farm ownership by Japanese amounted to about 30 percent of their total pre-war farm operations {and} ownership transfers to non-evacuees during and after evacuation has probably reduced these farm ownerships to less than a fourth of the total pre-war Japanese land holdings, including leaseholds . . . ." Few of the internees ever received full payment for their land.
https://www.washingtonpost.com/archive/opinions/1992/02/02/b...
This was further exposed in Korematsu vs. the US, where it was revealed that the Office of Naval Intelligence had prepared reports showing there was no actual threat, which they then hid from the courts when Japanese-American citizens sought redress through the justice system. Likewise, the FBI had already locked up or was monitoring anyone they thought was dangerous and had discredited all of the key justifications for internment:
https://www.justice.gov/archives/opa/blog/confession-error-s...
https://www.history.navy.mil/research/library/online-reading...