The characteristics of an empire (specifically a modern one) include a centralized government, a strong military, a dominant position in the global political theatre, and imperialist control over other nations/territories. A modern example of an empire is the United States.

The United States has a centralized federal government that exercises immense power over the people living under its nation-state borders. The United States has the third largest military in the world, with some analysts claiming it to be the most powerful military in the world. Certainly, US military spending vastly outpaces all other countries.

The United States is often designated as the most powerful country in the world. This designation is mostly related to military strength and economic power. However, the United States has one of the worst healthcare and education systems of any of the global North countries in the world.

The United States has colonial control over Puerto Rico, Guam, American Samoa, the US Virgin Islands, and the North Mariana Islands. All of these are classified as "unincorporated territories" of the United States—meaning that that fall under the jurisdiction of the United States, but they are not officially considered part of the US and are thus not completely subject to its laws and governance. Puerto Rico, in particular, has seen decades of popular resistance against the United States's imperialist control over the island of Puerto Rico.

The amount of US companies that have control over much of the world economic stage also contributes to the power of the United States as an empire. State and corporate power are a defining aspect of the US empire.

The characteristics of an empire include a strong, centralized government. Empires throughout history have emanated from a central location or base of power from which it projected power outward. That central location was usually a city-state like Rome or a kingdom like existed in Spain. The ruling regime at that location invariably sought to capture ever-greater tracts of territory to exploit resources (including humans of different ethnicities to be forced into slavery) and to increase its stature as an empire.

Another characteristic of an empire is a large, relatively modernized military. That always meant an army of soldiers. In many instances, it also meant a sea-going fleet. Without that large military, expansion against the will of those already occupying the territory in question would be impossible, as would controlling that territory in years ahead—years that stretched in some cases (Rome, Ottoman) to centuries. These militaries were often equipped with forms of weaponry unheard of by those they conquered.

Empires were sought for the purpose of attaining natural resources, but they were also enormously expensive to maintain. In fact, they were so expensive to maintain that they sometimes drove the emperor or king into bankruptcy. Raising, equipping and feeding a large military is very expensive and the more battles or wars that had to be fought to expand or retain the empire further strained the central government or regime’s treasure.

An extension of the desire for resources and the need for a large military is the construction of the infrastructure necessary to move resources and goods from the conquered territories to the center and military forces to far-flung destinations. It is well-known that the Roman Empire was so successful in part because of its facility for constructing paved roadways that enabled more efficient movement of goods and people. As with the costs of the military, however, the costs associated with constructing and maintaining a network of roads, bridges and, where relevant, railroads, was and remains considerable.

The military keeps the peace and puts down insurrections, but an empire has to be administered by professional civil servants. That is another characteristic of empires: bureaucracy. Records have to be kept, expenditures tracked, personnel administered, payrolls maintained, and logistics managed. That has to be done by trained personnel knowledgeable about the territory being administered and the myriad issues that will invariably arise.

While an empire can be maintained that entails more than one currency, set of laws and disparate systems of enforcement, the more commonality across the board the more efficiently the empire can be managed. Not only does such commonality or standardization increase efficiency, it helps to control the empire. By imposing a single common currency, for example, the central regime can better control economic activity but can also better control the population of the empire.

Centralized Power-Empires administer rule through a centralized system of leadership. Typically, empires were ruled by a monarch or a group of oligarchs. Centralized bureaucracies make significant decisions concerning the well-being of the empire.

Vast Territory-Empires typically rule over extensive portions of land and various territories. Some empires conquer neighboring territories and annex those areas, while others seek territories overseas and establish colonial rule.

Imperialist Agenda-Empires are ruled by individuals with imperialist agendas who wish to extend their country's influence through military force or diplomacy.

Diversity-Empires are made up of different ethnicities, nationalities, cultures, religions, and races.

Strong Military-Empires typically result from successful military conquests. Superior military strength allows various empires to conquer weaker nations which enable the centralized government to make territorial gains and expand the empire.

Depending on which book you are using for your class, the list of characteristics will vary. However, there are several characteristics which are necessary for a government to qualify as an empire.

• Centralized Leadership. Imperial rulers maintain control over large swaths of territory by constructing large bureaucracies based in the empire's capital. Imperial governments tend to resemble either a monarchy (rule by a king or queen) or an oligarchy (authoritarian rule by a small group of elites).
• Standardized Currency. Empires maintain a unified economy by making sure their subjects all use the same currency.
  
• Ethnic Diversity. Most empires have subjects from multiple civilizations and cultures.
• Expansionism. Empires seek to expand their power into new territories, either through military conquest or colonization. This expansionism allows them to increase the geographic size of their empires and acquire new subjects and natural resources.