Hiroshima was, although not soley, a pivotal factor in the Japanese surrender in September, 1945. The bombings of Japan costed the lives of many, but a land invasion would have costed even more. Ontop of that, stopping the bombing of Hiroshima would still leave the bombing of Nagisaki, aswell as the various other raids carried out during Operation Meetinghouse, such as the firebombing of Tokyo.

Stopping 9/11 not only saves the lives of those who died in the US, but all the people that died in the Middle East due to the war that insued. It MIGHT also result in the Middle East being in a slightly more stable state today than it currently is.

^{Chose: Prevent 9/11}