One of the more egregious errors of FDR in 1942, was to put thousands of American citizens (who happened to be Nisei Japanese) into US concentration camps and allowing private citizens and states like California take over all their property, homes and farms. The camps were terrible places where the men, women and children lived in tarpaper shacks, behind barbed wire fences guarded by US troops.
What makes it much worse is that it was quickly realized that they had made a mistake, that the camps were unnecessary, but for really sordid political reasons, they left the Japanese in those camps.
Many farmers from Oklahoma and Texas had fled the enormous region struck by the Dust Bowl to head to California (as depicted in The Grapes of Wrath by Steinbeck).
By the time it was realized that the Japanese were not a serious threat, then California Attorney General Earl Warren strongly argued to FDR against their release, figuring that the Dust Bowl refugees were both bigoted and wanted the jobs the Japanese had held, and if he kept them in those camps it would help his future political ambitions. He also figured that those wealthy Californians who had taken their land would also back him.
He did not officially repent these actions until 1977, eight years after he had retired as the Chief Justice of the Supreme Court.
Here is a map of the German-American internment camps, distinct from the German POW camps. Some 5000 Germans were deported from South American countries to be put in these camps as well.
I couldn’t find a ready map of Italian American internment camps.
Alaska Natives living in the Aleutian Islands were also interned during the war; Funter Bay was one such camp
It probably saved their lives.