How did a boy abandoned by his tribe become Genghis Khan?

He did it by outlasting people who were stronger than him, and by building something none of them had: a following based on loyalty instead of birth. Temüjin, the boy who would be Genghis Khan, was born around 1162 (historians argue about the year) as the eldest child of a Mongol chieftain. When he was eight his father died, and his family was abandoned by its tribe. The widow and her children lived like hunter-gatherers, collecting roots and nuts and catching fish.

From that low point he gathered friends. He found help from an older ally, Toghrul, and from Jamukha, a childhood blood brother, to win back his kidnapped wife Börte. People joined him because he was known as a fair and generous lord, and his shamans said heaven had chosen him for a great destiny. He was not unbeatable: Jamukha defeated him around 1187, and he probably spent years afterwards serving the Jin dynasty in North China.

Then he won. By 1206 he was sole ruler of the steppe, and at a great assembly he took the title Genghis Khan. He did not just rule the old tribes; he took them apart. Mongol men were reorganised into military units of tens, hundreds and thousands, a system meant to break tribal loyalty. Many of those commanders were sons of blacksmiths and herdsmen, promoted for what they did, not who they were.

The result was a state ready to march. From there he launched military campaigns that conquered large parts of China and Central Asia. The Mongols' own account of the man is surprisingly honest, down to the killing of his half-brother.