All you have to do is look at Okinawa. As a new prefecture of the Japanese Empire, even though the native populace didn't consider themselves Japanese, the fighting was fierce. A full one-third of the native populace were killed. Out of 119,000 Japanese soldiers, 112,000 were killed or forever sealed in their caves. The US lost 13,000 troops and another 34,000 wounded. The invasion of the Japanese mainland would have cost a projected 1 million American casualties and the near certain eradication of the Japanese race. The kicker, if those figures are not staggering enough, after Hiroshima, the Japanese government sealed off the area around the city, then sent in radio trucks to broadcast signals as if nothing had happen to the city. The atomic bombs were horrible, but 100% justifiable.