I've suggested that the US exist presently as an Empire. Others have disagreed pointing out the lack of success we have "occupying" other nations. Here's an interesting article touching on this subject.
The answer is that Washington’s empire extracts resources from the American people for the benefit of the few powerful interest groups that rule America. The military-security complex, Wall Street, agribusiness and the Israel lobby use the government to extract resources from Americans to serve their profits and power. The U.S. Constitution has been extracted in the interests of the security state, and Americans’ incomes have been redirected to the pockets of the 1 percent. That is how the American empire functions.