This is entirely supposition on my part, from someone far too young to have lived through any of it, but I suspect it's less that Japanese Americans looked different, and more that Japan was a non-Christian culture, which made it easier to dehumanize people of Japanese descent.

The Nazis might have been evil but at least they were "like us" in that they shared a common heritage, religion and linguistic root with Americans. Japan, meanwhile, was portrayed in American propaganda as an inscrutable hivemind run by a primitive death-cult.

You can see the same strange mistrust of non-Christian culture applied to Muslims in America today - even though the vast majority in the world are not violent terrorists, many Americans suspect that Islam taints and "radicalizes" the mind with evil in a way that Christianity doesn't.

Do you really believe that it was because Japan is dominantly a non-Christian culture and not because they look different? No, it was because they weren't white. And America has, for a very long time and even now, been painted as a mostly white and african american culture.

Even in modern Japan itself ironically enough, it's hard for some people to really picture non-white and non-african Americans as Americans. The word 外国人 (gaikokujin) really only applies to foreigners of European and African ancestry. I believe it's hard for them to picture those Americans as Americans simply because of the image that has been painted of the country.

Sincerely, A non-asian non-african non-white American interested in Japanese culture

>Do you really believe that it was because Japan is dominantly a non-Christian culture and not because they look different?

I believe it was both - they're two sides of the same coin. Look at the propaganda of the time - the Japanese were portrayed as being fundamentally inhuman in a way that Europeans weren't. The myth of the "inscrutable Oriental" has been around in the West for a very long time, the Japanese mind and morality were considered to be incomprehensible.

That Japanese Americans looked different probably made this xenophobia easier to act upon, though.

> suspect it's less that Japanese Americans looked different, and more that Japan was a non-Christian culture

Christianity and whiteness are surely connected in the cultural consciousness.