Over 2/3 of the Jewish population has been killed in 1933 and it was very violent how the Germans killed them. The U.S was jusified by stopping Hitler. More people could have died if the US didn't stop Hitler.
People that didn't live in Hiroshima or Nagasaki were happy when the bomb was dropped because they knew the war was over. Hiroshima and Nagasaki put an end to the war with the bomb. Without it the Japanese could have kept fighting.
In WW11 violence was not justified because there was so much fighting. Also in WW11 an atomic bomb did end a War but it was at a great cost. 185,000 people died at Hiroshima and Nagasaki and 110,000 died instantly.
Some historians argue violence is justified if it ends a War or stops things like death camps. Like during WW11 the allies and America stopped the Holocaust. I think sometimes violence is justified to end other violence
This article states that there was a lot of violence that started when President Roosevelt signed the declaration against Germany to start the war. he also felt the U.S needed to join to protect our allies, staying isolated was no longer possible.