The United States of America is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south. The state of Alaska is in the northwest of the continent, with Canada to its east and Russia to the west across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific. The country also possesses several territories, or insular areas, in the Caribbean and Pacific.
At 3.79 million square miles (9.83 million km²) and with about 305 million people, the United States is the third or fourth largest country by total area, and third largest by land area and by population.
The nation was founded by thirteen colonies of Great Britain located along the Atlantic seaboard. On July 4, 1776, they issued the Declaration of Independence, which proclaimed their independence from Great Britain and their formation of a cooperative union.
Geography and environment
The total land area of the contiguous United States is approximately 1.9 billion acres. Alaska, separated from the contiguous United States by Canada, is the largest state at 365 million acres. Hawaii, occupying an archipelago in the central Pacific, southwest of North America, has just over 4 million acres. After Russia and Canada, the United States is the world's third or fourth largest nation by total area, ranking just above or below China. The ranking varies depending on how two territories disputed by China and India are counted and how the total size of the United States is calculated. Including only land area, the United States is third in size behind Russia and China, just ahead of Canada.
The coastal plain of the Atlantic seaboard gives way further inland to deciduous forests and the rolling hills of the Piedmont. The Appalachian Mountains divide the eastern seaboard from the Great Lakes and the grasslands of the Midwest. The Mississippi–Missouri River, the world's fourth longest river system, runs mainly north–south through the heart of the country. The flat, fertile prairie of the Great Plains stretches to the west, interrupted by a highland region in the southeast. The Rocky Mountains, at the western edge of the Great Plains, extend north to south across the country, reaching altitudes higher than 14,000 feet (4,300 m) in Colorado. Farther west are the rocky Great Basin and deserts such as the Mojave. The Sierra Nevada and Cascade mountain ranges run close to the Pacific coast. At 20,320 feet (6,194 m), Alaska's Mount McKinley is the country's tallest peak. Active volcanoes are common throughout Alaska's Alexander and Aleutian Islands, and Hawaii consists of volcanic islands. The supervolcano underlying Yellowstone National Park in the Rockies is the continent's largest volcanic feature.
The federal government is composed of three branches:
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, and appoints the Cabinet 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, appoints, interpret laws, and can overturn laws they deem unconstitutional.