I've not done the proper homework on this, but from the little I know, his empress was his childhood sweetheart whom he married at the age of 16. Based on their tradition, they tend to have many women, and apparently they kidnapped a lot of beautiful women on the lands they conquered and had illegitimate children. Apparently 1/200 people in the world and 1/8 men in Asia have Mongolian DNA.

There are also stories on how women are treated as equals when it comes to power and leadership and he brought his daughters to war.

Jack Weatherford wrote another book called " The Secret History of the Mongol Queens - How the daughters of Genghis Khan rescued his empire"