Some states rule far beyond a single core territory. An empire is a large political unit that brings diverse peoples and lands under a single sovereign authority, usually through conquest or unequal alliance and maintained by a mixture of force, administration, and ideology.

Empires have taken many forms—land-based and maritime, multiethnic and settler, ancient and modern. Rome, the Mongols, the Ottomans, and the British each developed distinctive methods of rule. Tribute, taxation, military garrisons, and cultural prestige helped hold them together.

Empires rise, expand, and eventually fragment or transform. Their study raises questions about the management of diversity, the economics of extraction, and the identities formed under imperial conditions. The afterlives of empires remain visible in languages, borders, and political memories.

• Large multi-territorial political unit
• Rules diverse peoples under one authority
• Sustained by force, administration, and ideology
• Leaves lasting linguistic and territorial legacies