Most medieval kings desperately wanted sons. Sons inherited thrones but before they could they also had an awkward habit of rebelling against their fathers. History is full of kings brought down by ambitious sons. But Genghis Khan looked at the problem differently. Rather than treating his daughters as political afterthoughts, he married them into strategically important neighbouring kingdoms, required his sons-in-law to make them their chief wives, and then sent the sons-in-law off to fight in