Was USA justified in using 2 nuclear weapons during WWII?

Yeah, I think the atomic bombings were justified, at least in the context.  The US was preparing for invasions of the Japanese home islands.  They had just gotten off of a long campaign to capture Okinawa, a relatively small island which is Japanese but wasn't really considered part of the home islands (the Okinawans are their own ethnic group).  That had costs thousands of American lives IIRC and tens of thousands of Japanese lives.  The main islands like Honshu were much larger and would presumably be better defended with a Japanese military more motivated to fight.  Remember that in real life the Japanese didn't surrender after Hiroshima.  It took the US obliterating another city, and the specter that America could keep doing this over and over again, before the Japanese actually gave up.  Absent the nuclear weapons they probably would have fought on for a long long time.  American war planning expected the invasion of Japan to carry on well into 1946.  This would have cost a lot of American lives.  But it also would have cost a lot of Japanese lives.  It probably would have, in hindsight, cost more lives than were taken by the atomic bombs.