Genghis Khan: Madman or Genius?

Was Genghis Khan really a cold-blooded, ruthless murderer?  Or was he simply a brilliant and self-composed leader?  I have the notion that Genghis Khan was a genius and extremely talented military leader.  I get the sense of his killings being reasonable, not just done for the sake of doing so.  He was always able to justify a reason for attacking and killing other peoples, and if he was unable to, then he simply did not attack that specific tribe.  Genghis Khan was the ruler of the largest land empire ever to exist on the face of the earth.  He would be incapable of conquering so many different groups of people if he did it solely for the sake of killing them because more tribes would try to fight if they knew he would just murder them anyway.  People submitted to his whim if they knew his soldiers would be attacking.  If Genghis Khan really was just killing to shed blood, then he would have massacred all and any group of people, whether or not they resisted his power.  Khan was sensible to women and children.  He would not just slaughter the women and children of conquered peoples because he could; he let them go on with their business and even protect them from his own soldiers.