Hiroshima and Nagasaki are the reason why human being should not go into war, not to mention developing nuclear weapon, for ANY REASON.
Hiroshima bombing alone killed 140,000 (from 250,000 population jn Hiroshima at that time) people including innocent children, women, and elders. Its survivors affected by nuclear’s radiation (被爆者, hibakusha) and suffered from severe discrimination even until 3 decades after the bombing.
Japan was definitely guilty of starting the war in Pearl Harbor and killed 2,500 people but detonating a tiny sun in a very small town filled with mostly children, women, elders, and the ill certainly made the US just as bad as Japan. Even worse, probably.
(P.S: by comparison, 9/11 tragedy killed ‘only’ 3,000 people .. or 2004 Indian Ocean tsunami killed 230,000 across 14 countries)