Military power is not as powerful as ideological power. This can be seen through history. The Soviet Union's defeat in Afghanistan and the US defeat in Vietnam are two clear indicators that military power has its limits. To become truly powerful, a leader must capture a population's hearts and minds.
Genghis Kahn failed to capture people's hearts and minds. He forced his leadership on people and built an army of slaves. If he had been around today, an insurgency movement would have plagued his leadership and he would have been unable to build an empire.