An empire (from the Latin "imperium", denoting military command within the ancient Roman government) is a state that extends dominion over populations distinct culturally and ethnically from the culture/ethnicity at the center of power. Scholars still debate about what exactly constitutes an empire, and other definitions may emphasize economic or political factors.

Like other states, an empire maintains its political structure at least partly by coercion. Land-based empires (such as the Mongol Empire or the Achaemenid Persia) tend to extend in a contiguous area; sea-borne empires, also known as thalassocracies (the Athenian, Portuguese and the British empires provide examples), may feature looser structures and more scattered territories.

Definition

Empire contrasts with the example of a federation, where a large or small multi-ethnic state or even an ethnically homogeneous one relies on mutual agreement amongst its component political units which retain a high degree of autonomy. Additionally, one can compare physical empires with potentially more abstract or less formally structured hegemonies in which the sphere of influence of a single political unit (such as a city-state) dominates a culturally unified area politically or militarily. A second side of this same coin shows in potentially inherent tactics of divide and conquer by different factions ("the enemy of my enemy is my friend") and central intervention for the greater whole's benefit.

Compare also the concept of superpowers and hyperpowers. (Some commentators have seen the British Empire as a hyperpower, in its heyday as the largest empire in world history (covering about one quarter of the Earth's land surface) with established political, economical, financial, and scientific hegemony over the whole world.)

What constitutes an empire is subject to wide debate and varied definitions. An empire can be described as any state pursuing imperial policies, can be defined traditionally, or can be examined as a political structure. And in some cases the term "Empire" is also used when a ruler takes the title of "Emperor", even though the country involved has no other real reason to be considered an empire (for example, the short-lived "Central African Empire").

Unlike a well-defined nation-state, a multi-ethnic or colonial empire may have no natural shared language. Given that languages form an important part of administrative and cultural policy, the choice and use of language in empires can have considerable significance.

The Macedonians spread Greek as the unifying language of their empire and of its successor-states, but many of their subject populations continued to use Aramaic (as used by the preceding Persian Empire) as a lingua franca. The Romans imposed Latin thoroughly in Western Continental Europe, but less successfully in Britain and in the East. The Arab Empire succeeded in developing a cultural unity based on language and religion which continues to unify the Middle East. Spanish became well ensconced in Mexico, but less so in Paraguay and in the Philippines. The English language proved very successful in North America, but Russian did not supplant indigenous tongues in the Caucasus or in Central Asia.