From Infogalactic: the planetary knowledge core
The federal government of the United States is the central United States governmental body, established by the United States Constitution. The federal government has three branches: the legislative, executive, and judicial. Through a system of separation of powers and the system of "checks and balances," each of these branches has some authority to act on its own, some authority to regulate the other two branches, and has some of its own authority, in turn, regulated by the other branches. The policies of the federal government have a broad impact on both the domestic and foreign affairs of the United States. In addition, the powers of the federal government as a whole are limited by the Constitution, which, per the Tenth Amendment, reserves all power not directed to the National government, to the individual states, respectively, or "to the people". The seat of the federal government is in the federal district of Washington, D.C.