The nation was founded by thirteen colonies of Great Britain along the Atlantic seaboard. On July 4, 1776, they issued the Declaration of Independence, which announced their independence from Great Britain and their creation of a cooperative union. The disobedient states defeated Great Britain in the American Revolutionary War, the first successful colonial war of independence. The Philadelphia Convention adopted the current United States Constitution on September 17, 1787; its approval the following year made the states part of a single republic with a strong central government. The Bill of Rights, making up ten constitutional amendments guaranteeing many basic civil rights and freedoms, was approved in 1791.
In the 19th century, the United States got land from France, Spain, the United Kingdom, Mexico, and Russia, and took over the Republic of Texas and the Republic of Hawaii. Arguments between the farming-based South and industrial North over the growth of the institution of slavery and states' rights began the American Civil War of the 1860s. The North's victory prevented a permanent split of the country and led to the end of legal slavery in the United States. By the 1870s, the national wealth was the world's largest. The Spanish–American War and World War I confirmed the country's status as a military power. In 1945, the United States came out from World War II as the first country with nuclear weapons, a permanent member of the United Nations Security Council, and a founding member of NATO. The end of the Cold War and the breaking up of the Soviet Union left the United States as the only superpower. The United States participated in the Space Race that produced rapid advances in rocketry, materials science with the National Aeronautics and Space Administration. Apollo 11 was the first flight to send people to the moon. It was done by NASA, the American space group. It went up to space on July 16, 1969, carrying three astronauts: Neil Armstrong, Buzz Aldrin and Michael Collins. On July 20, 1969, Armstrong and Aldrin became the first humans to land on the moon, while Collins stayed in orbit around the Moon.
The United States is a federal republic of fifty states, a federal district, and several territories.
The land area of the contiguous United States is . Alaska, separated from the contiguous United States by Canada, is the largest state at . Hawaii, occupying an archipelago in the central Pacific, southwest of North America, is in area.
The United States is the world's third or fourth largest nation by total area (land and water), ranking behind Russia and Canada and 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 measured: calculations range from to to . Measured by 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 Chihuahua and Mojave. The Sierra Nevada and Cascade mountain ranges run close to the Pacific coast, both ranges reaching altitudes higher than 14,000 feet.
The United States, with its large size and geographical variety, includes most climate types. To the east of the 100th meridian, the climate ranges from humid continental in the north to humid subtropical in the south. The southern tip of Florida is tropical, as is Hawaii. The Great Plains west of the 100th meridian are semi-dry. Much of the Western mountains are alpine. The climate is dry in the Great Basin, desert in the Southwest, Mediterranean in coastal California, and oceanic in coastal Oregon and Washington and southern Alaska. Most of Alaska is subarctic or polar. Extreme weather is not unusual—the states bordering the Gulf of Mexico are prone to hurricanes, and most of the world's tornadoes happen within the country, mainly in the Midwest's Tornado Alley.
The U.S. ecology is considered "megadiverse": about 17,000 species of vascular plants occur in the contiguous United States and Alaska, and over 1,800 species of flowering plants are found in Hawaii, few of which occur on the mainland. The United States is home to more than 400 mammal, 750 bird, and 500 reptile and amphibian species. About 91,000 insect species have been described.
The Endangered Species Act of 1973 protects threatened and endangered species and their habitats, which are monitored by the United States Fish and Wildlife Service. There are fifty-eight national parks and hundreds of other federally managed parks, forests, and wilderness areas. Altogether, the government owns 28.8% of the country's land area. Most of this is protected, though some is leased for oil and gas drilling, mining, logging, or cattle ranching; 2.4% is used for military purposes.
A example of animals that are native to the United States such as opossums, raccoons, pumas and bears. Endangered animals in the United States include the jaguar, the California condor and the Florida panther.
Small trees and shrubs common in the United States are hackberry, hawthorn, serviceberry, blackberry, wild cherry, dogwood, and snowberry. Wildflowers bloom in all areas, from the seldom-seen blossoms of rare desert cacti to the hardiest alpine species. Wildflowers include forget-me-not, fringed and closed gentians, jack-in-the-pulpit, black-eyed Susan, columbine, and common dandelion, along with numerous varieties of aster, orchid, lady's slipper, and wild rose.
It is believed that the indigenous peoples of the continental United States, including the natives of Alaska, moved in from Asia. They began arriving twelve or forty thousand years ago, if not earlier. Some, such as the pre-Columbian Mississippian culture in the southeast, developed advanced farming, grand construction, and state-level communities. The native population of America decreased after Europeans arrived, and for different reasons, mostly sicknesses such as smallpox and measles.
In 1492, Genoese explorer Christopher Columbus, under contract to the Spanish crown, reached some Caribbean islands, making the first contact with the native people. On April 2, 1513, Spanish conquistador Juan Ponce de León landed on what he called "La Florida"—the first recorded European coming on what would become the U.S. mainland. Spanish settlements in the area were followed by ones in the present-day southwestern United States that drew thousands through Mexico. French fur traders established outposts of New France around the Great Lakes; France eventually claimed much of the North American interior, down to the Gulf of Mexico. The first successful English settlements were the Colony of Virginia in Jamestown in 1607 and the Pilgrims' Plymouth Colony in 1620. The 1628 chartering of the Massachusetts Bay Colony resulted in a wave of relocation; by 1634, New England had been settled by some 10,000 Puritans. Between the late 1610s and the American Revolution, about 50,000 convicts were shipped to Britain's American colonies. Beginning in 1614, the Dutch settled along the lower Hudson River, including New Amsterdam on Manhattan Island.