Previous replies :

https://www.reddit.com/r/AskHistorians/comments/2t89r7/why_didnt_the_us_bomb_tokyo/

https://www.reddit.com/r/AskHistorians/comments/1bd8en/what_was_the_next_city_the_usa_planned_on_using/

https://www.reddit.com/r/AskHistorians/comments/26r7rj/why_were_hiroshima_and_nagasaki_the_targets_of/

https://www.reddit.com/r/AskHistorians/comments/1w9dec/why_were_the_atomic_bombs_dropped_on_cities/

Some good links in those, especially the last one.