The United States is the world's oldest surviving federation. It is a constitutional republic and representative democracy, "in which majority rule is tempered by minority rights protected by law".The government is regulated by a system of checks and balances defined by the U.S. Constitution, which serves as the country's supreme legal document. For 2012, the US ranked 21st on the Democracy Index and 19th on the Corruption Perceptions Index.

• Legislative: The bicameral Congress, made up of the Senate and the House of Representatives, makes federal law, declares war, approves treaties, has the power of the purse,  and has the power of impeachment, by which it can remove sitting members of the government.
• Executive: The president is the commander-in-chief of the military, can veto legislative bills before they become law (subject to Congressional override), and appoints the members of the Cabinet (subject to Senate approval) and other officers, who administer and enforce federal laws and policies.
• Judicial: The Supreme Court and lower federal courts, whose judges are appointed by the president with Senate approval, interpret laws and overturn those they findunconstitutional.