The basis for the authority of the WWII Japanese regime, was the Shinto doctrine of Japanese racial descent from Amaterasu, the Sun Goddess, united by the Goddess' representative on Earth, the Emperor. Accordingly, they claimed that all ethnic Japanese were religiously and racially bound to loyalty to the Emperor. That presented a unique security threat within the USA.
The corollary, was that all non-Japanese ethnicities were excluded from that divinely ordained community. While Japanese-Americans were collected into camps during the war, non Japanese in Japan were overwhelmingly expelled or killed (thousands being used for Nazi-like experiments and weapons development, such as by Unit 731). The Japanese had been on a program of racially-driven massacres and atrocities in Asia, such as the Rape of Nanking, and the largest use of biological weapons against civilians during the 20th century (sometimes called the Asian Holocaust), before war was declared against the US.
Immediately upon declaring war, all Americans were rounded up in Japan (Man, Woman and Child), and calls went out to Japanese in America to uphold their sacred duty to join the fight on behalf of the Emperor. Japanese Americans were sorely inconvenienced by having to live in camps in the US during the war, while Americans in Japan and prisoners of war were routinely starved to death and executed by the tens of thousands.
