The Japs attacked and took over a lot of U.S. territories, the Philippines, for example, Guam, Wake Island, Attu, Kiska, they bombed Dutch Harbor (Alaska) and fire-bombed American forests, killing five Americans (but the fire-bombing was hushed up so as not to spread panic) - - I dunno, even for Americans there must have been SOME evidence that the Japs were out to get them.