What happened to the Mongol empire after Genghis Khan died?

Genghis Khan was succeeded by his son Ogedei. Ogedei further expanded the empire after death of Ogedei empire split into smaller but still large khanates, despite the fact that after the civil war there through next century there was a dominant great khan the Mongol Empire never became political whole again, the nearest to restore the empire was Tamerlane in late 14th c.