Actually, im kinda a history geek so... back then there was a war between US and Japan, they bombed us. And when we made OUR nuclear bombs, they surrendered. But we didn't take the apology and ended up blowing up a whole city in Japan.
In old anime shows, it used to be a LOT more violent. Take Shiki for example.
And just because it "didn't happen" doesn't mean its racist. You must be one of those people who thinks bringing up race in anything is racist, aren't you? If you are, go read up on some shit and open your eyes.