In the 13th Century, when Genghis Khan lived, birth control had not yet become a topical issue. Certainly not for those nomads traversing the wild steppes of Mongolia.
The Mongolian ruler was equally famed for his fertility as for his military conquests. Khan believed that to leave a lasting legacy (and sustain familial loyalty among Mongolian troops) a ruler had to produce offspring. In his case, many offspring.
Genghis Khan is reputed to have spawned hundreds of children. Most of them sons by different women. Recent studies by evolutionary geneticists suggest that there is now DNA evidence to support these claims. By tracing the Y-chromosome lineage back to that era and placing it in the region and time of Genghis Khan, the evidence suggests that Khan (and powerful male leaders like him), who would have prevailed over a social system that at the time permitted powerful male leaders to produce children with many women, is a strong candidate for the start of the male lineage which today spawns millions of men across Asia and, to a lesser degree, the wider world.