A country has established an empire when it has inflicted its military, economic, political, or cultural will on territories outside of its original realm. Empires tend to be driven by strong, advanced military institutions. They use the military to acquire territory that may be used for the acquisition of people, resources, and prestige. Empires tend to be ruled by a monarch, despot, or oligarchy and power is centralized in the capital.
The leader of an empire tends to organize a large bureaucracy with governors of different regions. Successful empires are able to efficiently manage a large number of people over vast distances. This can only be achieved with an organized government bureaucracy.
Empires tend to assimilate their subjects to the dominant culture. The reason for this is to create unity within the empire. This makes it easier to collect the tax or tribute that empires charge their conquered regions.