The justification for the bombings of Hiroshima and Nagasaki was to prevent the Allies from having to invade Japan by land, which could have resulted in an estimated million deaths, including casualties on both sides. Additionally, it spared millions of Japanese from potential enslavement under the Soviet Union, had Russian soldiers invaded the island.
The number of civilian casualties in Hiroshima and Nagasaki was comparable to the casualties caused by conventional air raids on other cities during that time. Nothing out of ordinary that might have impressed Joseph Stalin, who was used to murdering millions without a hiccup.
It is a tragic reality that in war, civilian casualties occur, but it is essential to remember that those responsible for initiating the conflict bear the greatest responsibility for all the lives lost. The US did not attack Japan unprovoked; it was Japan that initiated hostilities. Therefore, Japanese leaders are accountable for all the casualties that followed.
Similarly, in the case of Ukraine and Russia, it was Russia that invaded Ukraine in 2014. The Russian regime must be held fully responsible for all the lives lost during this war.
In summary, while the bombings of Hiroshima and Nagasaki had devastating consequences, they were undertaken to avoid an even greater loss of life through a potential land invasion.