Earlier quoted context omitted.
Was the U.S. entering WW2 after Pearl Harbor just systematic barbarism in retribution?
Honest question — how else would you describe dropping a nuclear bomb each on Hiroshima and Nagasaki, cities full of civilians, causing "between 129,000 and 226,000" deaths (source: Wikipedia)? Those were not military targets.
.. a rush job to test two different designs for a new weapon, snuck in before the very same cities were destroyed much more cheaply with conventional heavy explosives and incideriaries, just as 72 Japanese cities had already been destroyed.
That answer because you asked about the nuclear bombs rather than the total destruction of complete cities in the European and Japanese theatres.
You can compare the death toll from the Tokyo firebombings to that in either Hiroshima or Nagasaki, you can look up the names of the other 71 cities destroyed and you can find the full list of planned targets (now long forgotten save for H & N) in the archives.