The United States Constitution defines a federal system of government in which certain powers are delegated to the national government and others are reserved to the states. The national government consists of executive, legislative, and judicial branches that are designed, through separation of powers and checks and balances, to ensure that no one branch of government is able to subordinate the other two branches. All three branches are interrelated, each with overlapping yet quite distinct authority.
Since its ratification in 1788 there have been 27 amendments to the Constitution. The first 10 amendments, adopted in 1791 and known collectively as the Bill of Rights, established a number of individual liberties, including speech, religion, the press, and the rights of the criminally accused. Among other important amendments are the Thirteenth (1865), which abolished slavery; the Fourteenth (1868), which granted citizenship rights to former slaves and guaranteed to every citizen due process and equal protection of the laws; the Fifteenth (1870), which granted voting rights to former male slaves; the Seventeenth (1913), which provided for the direct election of U.S. senators; the Nineteenth (1920), which established woman suffrage; the Twenty-Second (1951), which limited a president to a maximum of two elected terms in office; and the Twenty-Sixth (1971), which extended voting rights to all citizens 18 years of age or older. Amending the Constitution requires a proposal by a two-thirds vote of both houses of Congress or by a national convention, followed by ratification by three-fourths of the state legislatures or state conventions.
The executive branch is headed by the president, who must be a natural-born citizen of the United States, at least 35 years old, and a resident of the country for at least 14 years. The president's official residence and office is the White House in Washington, D.C. The formal constitutional responsi