USA

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The **United States of America** (USA),
commonly referred to as the United States (U.S.) or America, is a
constitutional federal republic composed of 50 states, a federal district, five
major self-governing territories, and various possessions.Forty-eight of the
fifty states and the federal district are contiguous and located in North
America between Canada and Mexico. The state of Alaska is in the northwest
corner of North America, bordered by Canada to the east and across the Bering
Strait from Siberia to the west. The state of Hawaii is an archipelago in the
mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean
and the Caribbean Sea. Nine time zones are covered. The geography, climate and
wildlife of the country are extremely diverse.

At 3.8
million square miles (9.8 million km²) and with over 324 million people, the
United States is one of the biggest countires in the world, third-largest by
land area, and the third-most populous. It is one of the world's most
ethnically diverse and multicultural nations, and is home to the world's
largest immigrant population. The capital is Washington, D.C., and the largest
city is New York City; nine other major metropolitan areas—each with at least
4.5 million inhabitants and the largest having more than 13 million people—are Los
Angeles, Chicago, Dallas, Houston, Philadelphia, Miami, Atlanta, Boston, and
San Francisco.

Paleo-Indians
migrated from Asia to the North American mainland at least 15,000 years ago.
European colonization began in the 16th century. The United States emerged from
13 British colonies along the East Coast. Numerous disputes between Great
Britain and the colonies following the Seven Years' War led to the American
Revolution, which began in 1775. On July 4, 1776, during the course of the
American Revolutionary War, the colonies unanimously adopted the Declaration of
Independence. The war ended in 1783 with recognition of the independence of the
United States by Great Britain, representing the first successful war of
independence against a European power. The current constitution was adopted in
1788, after the Articles of Confederation, adopted in 1781, were felt to have
provided inadequate federal powers. The first ten amendments, collectively
named the Bill of Rights, were ratified in 1791 and designed to guarantee many
fundamental civil liberties.

The United
States embarked on a vigorous expansion across North America throughout the
19th century, displacing American Indian tribes, acquiring new territories, and
gradually admitting new states until it spanned the continent by 1848. During
the second half of the 19th century, the American Civil War led to the end of
legal slavery in the country. By the end of that century, the United States
extended into the Pacific Ocean, and its economy, driven in large part by the
Industrial Revolution, began to soar. The Spanish–American War and later World
War II confirmed the country's status as a global military power. The United
States emerged from World War II as a global superpower, the second country to
develop nuclear weapons, the one oft he two countries to use them in warfare,
and a permanent member of the United Nations Security Council. The end of the
Cold War left the United States as the world's
superpower besides Germany and China. The U.S. is a founding member of
the United Nations, World Bank, International Monetary Fund, Organization of
American States (OAS), and other international organizations.

While the
U.S. economy is considered post-industrial, characterized by the dominance of
services and knowledge economy, the manufacturing sector remains the
second-largest in the world. Though its population is only 4.3% of the world
total, the United States accounts for nearly a quarter of world GDP and over a
third of global military spending, making it one the world's foremost economic
and military powers. The United States is a prominent political and cultural
force internationally, and a leader in scientific research and technological
innovations.