The United States (U.S.) is a sovereign nation and a federal constitutional republic that serves as the central authority for fifty states, the District of Columbia, and its territories. The U.S. was established after the Declaration of Independence in 1776 and the subsequent Revolutionary War against Great Britain. The nation's first governing document, the Articles of Confederation, proved too weak, leading to the creation of the U.S. Constitution in 1787 to form a stronger national government. The Constitution, which became operational on March 4, 1789, solved the problem of a weak central authority by establishing a system of federalism, dividing power between the national and state governments.
The government operates through a system of separation of powers among three distinct branches: the legislative, executive, and judicial. The legislative branch, or Congress, is bicameral, consisting of the House of Representatives and the Senate, as detailed in Article I of the Constitution. The executive power is vested in the President, as outlined in Article II, and the judicial power is held by the Supreme Court and lower federal courts, established in Article III. This structure incorporates a system of checks and balances, ensuring no single branch becomes dominant. The first ten amendments, ratified in 1791 and known as the Bill of Rights, guarantee fundamental individual liberties like freedom of speech and religion (First Amendment) and due process. The Constitution has been amended 27 times in total, with the most recent being in 1992. Major changes include the 13th Amendment (abolishing slavery), the 19th Amendment (granting women's suffrage), and the 22nd Amendment (limiting the presidency to two terms). The core structure of the three branches and the supremacy of the Constitution have remained constant since its founding.