US schools teach that the atom bombs were used as an alternative to an invasion of Japan. The numbers said millions would die on both sides if the Allies staged an invasion. Instead, the largest estimated loss ended up being 226,000 Japanese.

The second bomb was dropped because the military leadership in Japan couldn't believe the destruction from one bomb wasn't just another night raid that was super effective and refused to surrender. Then the second bomb dropped, and immediate unconditional surrender was issued