The United States of America

The United States Of America

The United States of America (USA or U.S.A.), commonly called the United States (US or U.S.) and America, is a federal republic consisting of fifty states and a federal district. The 48 contiguous states and the federal district of Washington, D.C. are in central North America between Canada and Mexico. The state of Alaska is west of Canada and east of Russia across the Bering Strait, and the state of Hawaii is in the mid-North Pacific. The country also has five populated and nine unpopulated territories in the Pacific and the Caribbean.

At 3.79 million square miles (9.83 million km2) and with around 315 million people, the United States is the third-or fourth-largest country by total area and the third-largest by both land area and population. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The geography and climate of the U.S. is also extremely diverse, with deserts, plains, forests, and mountains that are home to a wide variety of species.

Paleo-indians migrated from Asia to what is now the United States mainland around 15,000 years ago. After 1500, Old World diseases introduced by Europeans greatly reduced their populations. European colonization began around 1600 and came mostly from England. The United States emerged from thirteen British colonies located along the Atlantic seaboard. Disputes between Great Britain and the American colonies led to the American Revolution. On July 4, 1776, delegates from the thirteen colonies unanimously issued the Declaration of Independence, which established the United States of America. The American Revolutionary War, which ended with the recognition of independence of the United States from the Kingdom of Great Britain, was the first successful war of independence against a European colonial empire. The current Constitution was adopted on September 17, 1787; 27 Amendments have since been added to the Constitution. The first ten amendments, collectively named the Bill of Rights, were ratified in 1791 and guarantee many fundamental civil rights and freedoms.

Driven by the doctrine of manifest destiny, the United States embarked on a vigorous expansion across North America throughout the nineteenth century. This involved displacing native tribes, acquiring new territories, and gradually admitting new states. The American Civil War ended legalized slavery in the United States. By the end of the nineteenth century, the United States extended into the Pacific Ocean, and its economy was the world's largest. The Spanish–American War and World War I confirmed the country's status as a global military power. The United States emerged from World War II as a global superpower, the first country with nuclear weapons, and a permanent member of the United Nations Security Council. The end of the Cold War and the dissolution of the Soviet Union left the United States as the sole superpower.

The United States is a developed country and has the world's largest national economy, with an estimated 2012 GDP of $15.6 trillion – 19% of global GDP at purchasing-power parity, as of 2011. The per capita GDP of the U.S. was the world's sixth-highest as of 2010, although America's income inequality was also ranked highest among OECD countries by the World Bank. The economy is fueled by an abundance of natural resources, a well-developed infrastructure, and high productivity; and while its economy is considered post-industrial it continues to be one of the world's largest manufacturers. The country accounts for 39% of global military spending, and is a leading economic, political, and cultural force in the world, as well as a leader in scientific research and technological innovation.