Although Khan certainly united many, many tribes and clans which were dispersed across Asia during his lifetime, I think any good leader will know you can't manage to conquer half the world without some torture, a few massacres and of course, a great deal of be-headings.

It's estimated that under Genghis Khan's rule about 11.1% of the worlds population died including the Mongol warriors and their enemies.  That's about 40 million people! That's also more than Hitler and Joseph Stalin put together.  Well anyone who killed their half brother in a dispute at the age of ten obviously has some cold blood within them.