How empires begin and end

It has always puzzled me how a small, technologically advantaged force can dominate vast multitudes in far reaches of the planet. It’s the story of empire: The Romans extending their rule across Europe and the Mediterranean. Cortés and a few hundred Spaniards conquering the powerful and warlike Aztecs, who had created an empire of their own. And more recently, the British building an empire on which the sun never set, its crown jewel being India.

In most cases the story of empire is one of the...