There should be a TV show on Genghis similar to the Vikings show on Ragnar’s Viking conquests. I would rate Genghis as the #1 Bad Ass of all time. While he did act savage at times, he was the most pragmatically brilliant and successful leader I have ever read about.
Where does Truman and Hiroshima fit into your analysis. I firmly believe that if a leader takes his armed forces into battle the leader has the duty to do all that is necessary to defeat the enemy while minimizing harm to his armed forces.