A great book to read might be "Genghis Khan and the Making of the Modern World" It's a great read really discussing Genghis Khan's life, descendants and the Mongols in general. According to the book Genghis Khan's father died at a young age and his mother and step mother and brothers were abandoned by their tribe to survive on their own. Genghis Khan had an older brother who was head of their family as eldest. Genghis Khan simply refused to be subordinate and with his younger brother killed him. He was only about 10 yrs old when he killed his older brother. According to the book this showed how he refused to follow and desired leadership. Regarding how he could become the greatest conqueror, he was able to unite the many tribes of Mongolia which enabled him to conquer. The book really illustrates how much of a tactical leader he was.