Yes it was justified
It was necessary to stop the war.
Yes, the atomic bomb the U.S dropped on both Hiroshima and Nagasaki was brutal, but Japan was going to invade the United States and we were running out of supplies, people, guns, bullets and so on.
So it was either the bomb or America has to lose the war.
Also, Japan didn't want to surrender when the U.S. gave them chances to.
So in the end after the United States of America bombed Hiroshima and Nagasaki, Japan finally surrendered.
Hope I had helped~