United States

The United States of America (USA), commonly known as the United States (U.S. or US) or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. The capital is Washington, D.C., and the most populous city is New York City. Most of the country is located contiguously in North America between Canada and Mexico.

Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century. The United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies led to the American Revolution—open war began in 1775, and the Declaration of Independence was issued in 1776. The war ended in 1783 with the United States becoming the first country to gain independence from a colonial empire. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties. The United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, and gradually admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery. By the end of the century, the United States had reached the Pacific Ocean, and its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power. The United States emerged from the Great Depression as a global superpower, the first country to develop nuclear weapons and a founding member of the United Nations. Since then the United States has been competing with the Soviet Union for global dominance in the Cold War.

The United States is a federal republic and a representative democracy. It is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States (OAS), and other international organizations. It is a highly developed country, with the world's largest economy by nominal GDP and largest economy by PPP. Despite income and wealth disparities, the United States continues to rank very high in measures of socioeconomic performance, including average wage, median income, median wealth, human development, per capita GDP, and worker productivity. It is the foremost military power in the world and is a leading political, cultural, and scientific force internationally.

Etymology
In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci (Latin: Americus Vespucius). The first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq., to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort. The first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776.

The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the 'United States of America'". The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be 'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence. This draft of the document did not surface until June 21, 1776, and it is unclear whether it was written before or after Dickinson used the term in his June 17 draft of the Articles of Confederation.

The short form "United States" is also standard. Other common forms are the "U.S.", the "USA", and "America". Colloquial names are the "U.S. of A." and, internationally, the "States". "Columbia", a name popular in poetry and songs of the late 18th century, derives its origin from Christopher Columbus; it appears in the name "District of Columbia", many landmarks and institutions in the Western Hemisphere bear his name, including the country of Colombia.

The phrase "United States" was originally plural, a description of a collection of independent states—e.g., "the United States are"—including in the Thirteenth Amendment to the United States Constitution, ratified in 1865.The singular form—e.g., "the United States is"—became popular after the end of the American Civil War. The singular form is now standard; the plural form is retained in the idiom "these United States". The difference is more significant than usage; it is a difference between a collection of states and a unit.

A citizen of the United States is an "American". "United States", "American" and "U.S." refer to the country adjectivally ("American values", "U.S. forces"). In English, the word "American" rarely refers to topics or subjects not directly connected with the United States.

Indigenous peoples and pre-Columbian history
It has been generally accepted that the first inhabitants of North America migrated from Siberia by way of the Bering land bridge and arrived at least 12,000 years ago; however, increasing evidence suggests an even earlier arrival. After crossing the land bridge, the first Americans moved southward along the Pacific coast and through an interior ice-free corridor between the Cordilleran and Laurentide ice sheets. The Clovis culture appeared around 11,000 BC, and is considered to be an ancestor of most of the later indigenous cultures of the Americas. The Clovis culture was believed to represent the first human settlement of the Americas. Over the years, more and more evidence has advanced the idea of "pre-Clovis" cultures including tools dating back about 15,550 years ago. It is likely these represent the first of three major waves of migrations into North America.

Over time, indigenous cultures in North America grew increasingly complex, and some, such as the pre-Columbian Mississippian culture in the southeast, developed advanced agriculture, grand architecture, and state-level societies. The Mississippian culture flourished in the south from 800 to 1600 AD, extending from the Mexican border down through Florida. Its city state Cahokia is considered the largest, most complex pre-Columbian archaeological site in the modern-day United States. In the Four Corners region, Ancestral Puebloans culture developed as the culmination of centuries of agricultural experimentation, which produced greater dependence on farming. Three World Heritage Sites in the United States are credited to the Pueblos: Mesa Verde National Park, Chaco Culture National Historical Park, and Taos Pueblo. The earthworks constructed by Native Americans of the Poverty Point culture in northeastern Louisiana have also been designated a World Heritage site. In the southern Great Lakes region, the Iroquois Confederacy (Haudenosaunee) was established at some point between the twelfth and fifteenth centuries.

The date of the first settlements of the Hawaiian Islands is a topic of continuing debate. Archaeological evidence seems to indicate a settlement as early as 124 AD.

Effects on and interaction with native populations
With the progress of European colonization in the territories of the contemporary United States, the Native Americans were often conquered and displaced. The native population of America declined after Europeans arrived, and for various reasons, primarily diseases such as smallpox and measles.

While estimating the original native population of North America at the time of European contact is difficult, an attempt was made in the early part of the twentieth century by James Mooney using historic records to estimate the indigenous population north of Mexico in 1600. Anthropologist Henry F. Dobyns believed that the populations were much higher, suggesting 1,100,000 along the shores of the gulf of Mexico, 2,211,000 people living between Florida and Massachusetts, 5,250,000 in the Mississippi Valley and tributaries and 697,000 people in the Florida peninsula.

The first interaction between Europeans and Native Americans was made by the Norsemen. A number of surviving Norse sagas provide information regarding The Maritimes and its indigenous people. The Norse attempted to settle in North America about 500 years before Columbus.

In the early days of colonization, many European settlers were subject to food shortages, disease, and attacks from Native Americans. Native Americans were also often at war with neighboring tribes and allied with Europeans in their colonial wars. At the same time, however, many natives and settlers came to depend on each other. Settlers traded for food and animal pelts, natives for guns, ammunition and other European wares. Natives taught many settlers where, when and how to cultivate corn, beans, and squash. European missionaries and others felt it was important to "civilize" the Native Americans and urged them to adopt European agricultural techniques and lifestyles.

European settlements
g

Independence and expansion (1776–1865)
g

Civil War and Reconstruction era
s

Further immigration, expansion, and industrialization
d

World War I and the Great Depression
a

Contemporary History
e

Geography, climate, and environment
f

Wildlife
q

Population
d

Major population areas
f

=== Language === s

Religion
f