Alexander the Great
In just over a decade, Alexander of Macedon conquered the entire Persian Empire and pushed to the edge of India, never losing a battle, before dying of fever at thirty-two with no plan for who would follow. His generals promptly tore the empire apart. But the Greek culture he scattered from Egypt to Afghanistan — the Hellenistic world — fused with local traditions and outlived him by centuries, making Greek the common tongue of the eastern Mediterranean. He is the archetype of the conqueror whose reach vastly exceeds his grip: brilliant at winning, fatally unready to hold.
A state's commitments outrun the resources and logistics needed to hold them; the margin fails first.