All it took was a presidential executive order to start the process of rounding up those and other Americans and put them in segregated camps.
The Japanese especially were vastly out numbered and were dealing with the generation of whites who still carried out lynchings. I don't know what gun ownership rates at the time was among the Japanese and others interned, but either way it's a tough call. Go peacefully and gamble on the mercy of your captors, or resist and go out guns blazing and give them even more reasons to mistreat these groups.
Americans now personally own over 400 million firearms and supposedly billions of rounds of ammunition. I think a good number of modern American's realize the government would have no problem doing to them what they did to those American's in the 1940's.
https://en.wikipedia.org/wiki/Executive_Order_9066