The United States is a constitutional federal republic with a presidential system. Federal power is divided among Congress, the executive branch led by the president, and the Supreme Court and lower federal courts. States retain broad authority over subjects not assigned to the federal government, while local governments provide services such as policing, education, transportation, housing, and public health.
Elections occur at federal, state, and local levels. Nearly all citizens aged 18 and older may vote, although some states restrict voting by people convicted of felonies and residents of U.S. territories lack full national voting rights. The president is the major exception to direct election: voters choose pledged electors who formally select the president through the Electoral College.
Democrats and Republicans have dominated national politics since the nineteenth century. The first-past-the-post system, single-member districts, ballot-access rules, and strategic voting make it difficult for third parties to compete. Yet neither major party has a strong national authority controlling every official, leaving room for factions and dissent.
American politics has changed dramatically. Suffrage expanded, secret ballots replaced public voting, the New Deal transformed federal responsibilities, and civil-rights legislation reshaped party coalitions. Since the 1990s, ideological and emotional polarization have intensified, accompanied by growing concern about election denial, democratic backsliding, campaign finance, special-interest influence, and gerrymandering.
Representation remains contested. Women, racial and ethnic minorities, LGBTQ people, territorial residents, and others often hold fewer offices than their share of the population would suggest. Critics argue that the Senate, Electoral College, district maps, and concentrated wealth can produce policies that do not reflect majority preferences. Reform proposals include voting changes, congressional term limits, and new rules for Supreme Court appointments.