OTOH, one of the German invasions in this article did involve 8 naturalized US citizens.
As you know, the west coast was designated a ‘military area’ by both Canada and the US out of fears that the Japanese were going to launch a full-scale land invasion following Pearl Harbor. The US coast was controlled by Western Command, US Army; curfews and blackouts were imposed. Three reasons given for removing the Japanese from a potential war zone was that they wouldn’t be able to be discerned from invading Japanese, their loyalties remained with the Emperor and they would turn and fight with invading Japanese, and, those Americans who lost their sons in the war might just take it out on their Japanese neighbor (and a fourth would be the state Govs asked for it and a fifth would be actual intercepts by the military, covered upthread).
Internment centers were intended to be temporary until deportation after the war. Relocation was upheld by the Supreme Court in Hirabayashi v The United States, 1943 and Korematsu v The United States, 1944. (see also Pearl Harbor Commission)
The Loyalty Oath:
Roosevelt lifted the naturalized Japanese enlistment ban in early 43. A call for volunteers went out to the camps and a loyalty questionnaire began to circulate. Roosevelt’s objective was countering Japanese racist propaganda by making a show of enlisted Japanese-American troops fighting right alongside Americans against the evil Emperor. The questionnaire would satisfy two purposes: to fulfill the “individual examination of loyalties” requirement, and as further propaganda against Japan ( see?! 97.5% - take that, Japan!). Unfortunately, the results of the questionnaire lent fuel to the argument to keep ‘disloyal’ residents detained and lessened the argument that people were detained for no valid reason.
Of the 120,000 men women and children interned, 40,000 were born in Japan and ineligible for enlistment and 30,000 were children and a few thousand men were criminals already. Of the approximately 20,000 remaining men 18-45, almost 20% refused to sign an allegiance to the US - even though doing so meant they could take their family and leave their camp for points east. Over 5,500 outright renounced their American citizenship. Some even parroted Japan propaganda and voiced refusal to ‘help white soldiers’. By the time the US started to wind down the camps, less than 2,000 had signed the oath and enlisted. In contrast, 10,000 Japanese volunteered in Hawaii, and volunteers were high across the rest of the US.
Justice Douglas made it clear in 44 that loyal citizens should be released but 10,000 adult men refusing to pledge loyalty fueled rumor and intense suspicion in the US. How could these men be trusted if the war turned sour? We didn’t separate families (like Canada), so if the man refused, his family stayed with him. Were it not for legislation after the war that allowed most of them to stay, those 10,000 or so families would have been deported - because they refused to sign a loyalty oath.
https://thebluereview.org/wwii-japanese-incarceration/
http://www.pbs.org/thewar/at_war_democracy_japanese_american.htm
http://encyclopedia.densho.org/Japanese_Americans_in_military_during_World_War_II/
https://en.wikipedia.org/wiki/Internment_of_Japanese_Americans
https://www.nps.gov/manz/learn/historyculture/japanese-americans-at-manzanar.htm