I’ll make this simple for you: America did not want to be involved in the war that Japan forced them into. They were suffering mass casualties in the pacific theater. The Japanese were torturing US POWs and using suicide kamikaze attacks against US naval vessels which also resulted in huge numbers of casualties.

They figured nuking these guys a couple of times would finally get them to fucking stop, and what do you know? It did. Mission accomplished. End of story.

They were justified because doing that allowed them to finally stop getting killed and tortured by the nation that attacked them first. I too hate the fact that the Japanese imperial government put its people in such peril with so little regard for their safety.