The use of atomic bombs against civilians was a logical outgrowth of the industrialization of war. WWI showed the world how the mass production of death could be organized to kill large numbers of soldiers. World War II advanced the technology to include the deaths of large numbers of civilians.

Ironically, the bomb was originally developed because it was feared that Germany was developing one. The international science community was well aware that German physicist Werner Heisenberg was quite capable of leading such a project.

For a variety of reasons (one of which was that Hitler believed modern physics was “Jewish science"), Germany never got much beyond a heavy water plant in Norway. The plant was attacked by British agents and Norwegian partisans and later damaged in bombing raids. There is some circumstantial evidence that Heisenberg himself deliberately dragged his feet on doing bomb research.

The American science team was led by Robert Oppenheimer who had strong leftwing connections and a number leftists worked on the A-bomb and saw it as part of the anti-fascist movement. Later some were horrified when it was dropped on Japan. Some had even thought (naively) that since they had developed the thing, that they should have some say in how it used.

The dropping of the bombs on Japan was controversial at the time. Even Ike had misgvings. Human motivations are complex and I think the decision to use the A-Bomb against Japan flowed from a number of factors. After the horrors of the Rape of Nanking, the death camps, the London Blitz, Dresden,etc., what was one more atrocity?

Personally, I think dropping the bombs was morally wrong, but if I had been Truman after years of endless mass destruction, I probably would have used them too. War does not turn very many people toward sainthood. I once saw the Trinity site from atop a mountain in New Mexico. The scar is still visible from the first nuclear explosion. The moral scar upon our nation is still visible as well......