In Executive Order 9066, FDR hands over authority to the secretary of war and all of his war people to plot out specific zones of the country and label them "military areas." What kinds of specific zones, you ask? Oh, nothing much…just essentially the entire West Coast of the continental United States.
Within these zones, the secretary of war is allowed to make the rules, particularly when it comes to who can stay and who has to scram. FDR includes a certain amount of responsibility with this power by instructing Mr. Secretary and company to provide basic amenities for the people they kick out of their special zones.
He also tells the rest of his federal government that they're supposed to aid the secretary of war in carrying out the creation and maintenance of the military areas. E.O. 9066 is sort of like a parent giving one of his children a goldfish, telling him to take care of said fish, and then telling the other goldfish-less children to help him do it, too.
Well, we all know what happens to that goldfish in the end.
People act in extreme ways under extreme conditions. Anti-Japanese racism was an unfortunate product of the time, but war hysteria during World War II was motivated by very real fear, and the president responded in the manner he saw fit for the circumstances.
The Constitution should never be manipulated in the name of injustice. Wartime or not, E.O. 9066 was a corruption of the law based more on personal agendas than a concern for national security.
The Imperial Japanese Navy Air Service bombs the U.S. military base at Pearl Harbor, Hawaii Territory, drawing America into World War II. Back on the mainland, xenophobic war hysteria and anti-Japanese racism spread like a California wildfire.
E.O. 9066 issues special permissions for the secretary of war and his associates to create military zones that they fully control—all in consideration of national defense.
Now, that's a lot of power.
Some of that power includes being able to determine who occupies those zones and who doesn't. This means that certain people who are considered "dangerous" to the peace and security of the nation can be forcibly expelled from the military areas. Most of the people expelled were Japanese Americans.
If such drastic measures seem unfair, it's because they are. Super unfair. But FDR is careful to cite legal and historical precedents to justify and uphold his declaration.
E.O. 9066 gives the secretary of war power to create special military exclusion areas and unjustly sweep away suspicious citizens (i.e., 120,000 Japanese Americans) from the West Coast and dump them in inland internment camps.
History would remember this as the U.S. government acting very much in the wrong.