While Hiroshima was justified, Nagasaki was due to the pressures of war. Have seen and read of the events after Hiroshima and before Nagasaki.
On August 6, 1945, the phone lines to Hiroshima went dead. A minor corporal was sent to investigate. He arrived the next morning, the 7th. He spent that day being astonished by what he saw. He arrived back at headquarters on the 8th. He spent the morning and afternoon talking with progressively higher officers. Eventually the military leaders agreed surrender was the only option. Unfortunately, the Emperor had gone to bed and they decided to wait until the next day, the 9th.
Meanwhile in Washington D.C., Truman was being pressured to drop the second bomb. Finally, with no word that was the decision. Another day would have made all the difference.
The pressures of war and difficult to defuse, especially when the end is in sight.