The United States of America (USA), often known as the United States (U.S.) or America, is a federal republic comprised of fifty states, a federal district, five main self-governing territories, and other possessions. In North America, between Canada and Mexico, 48 of the fifty states and the federal district are continuous. Alaska is located in the extreme northern region of North America, sharing a land border with Canada and separated from Russia by the Bering Strait. Hawaii is an archipelago located in the central Pacific. The territories are dispersed across the Pacific and Caribbean oceans. There are nine time zones covered. The country’s topography, climate, and fauna are all very varied.
The United States is the world’s fourth-largest nation by total size (and fourth-largest by land area) and third-most populated country, covering 3.8 million square miles (9.8 million km2) and home to over 324 million people. It is one of the most ethnically diverse and cosmopolitan countries on the planet, with the world’s biggest immigrant population. Urbanization increased to more than 80% in 2010, resulting in the growth of megaregions. Washington, D.C. is the capital, and New York Metropolis is the biggest city; the other major metropolitan regions, all of which have a population of approximately five million or more, include Los Angeles, Chicago, San Francisco, Boston, Dallas, Philadelphia, Houston, Miami, and Atlanta.
Paleo-Indians arrived in North America from Asia at least 15,000 years ago. Colonization by Europeans started in the sixteenth century. The United States was formed by the merger of thirteen British colonies along the East Coast. Numerous conflicts between Great Britain and the colonies in the aftermath of the Seven Years’ War precipitated the start of the American Revolution in 1775. On July 4, 1776, while the colonies were engaged in the American Revolutionary War, delegates from the thirteen colonies approved the Declaration of Independence unanimously. The war concluded in 1783 with Great Britain’s acknowledgment of the United States’ independence. It was the first victorious independence war against a European colonial empire. The present constitution was established in 1788, when it was determined that the Articles of Confederation, ratified in 1781, offered insufficient governmental powers. The first 10 amendments, commonly referred to as the Bill of Rights, were adopted in 1791 and were intended to protect a broad range of basic civil rights.
Throughout the nineteenth century, the United States expanded rapidly throughout North America, displacing American Indian tribes, gaining new territory, and progressively admitting new states until it covered the continent by 1848. The American Civil War in the second part of the nineteenth century resulted in the abolition of legal slavery in the nation. By the turn of the twentieth century, the United States had expanded into the Pacific Ocean, and its economy had soared, owing in large part to the Industrial Revolution. The Spanish–American War and World War I established the country’s military might on a worldwide scale. The US emerged from World War II as a worldwide powerhouse, the first nation to develop nuclear weapons, the first one to deploy them in combat, and a permanent member of the United Nations Security Council. It is a founding member of the Organization of American States (UAS) and a number of other regional and international organizations. After the Cold War ended and the Soviet Union disbanded in 1991, the United States became the world’s only superpower.
The United States is a highly developed nation with the biggest economy in the world in terms of nominal GDP. It scores highly on many socioeconomic performance indicators, including average salary, human development, per capita GDP, and per person productivity. While the US economy is considered post-industrial, with a strong emphasis on services and information, the manufacturing sector remains the world’s second biggest. While the United States’ population is just 4.4 percent of the worldwide total, it contributes for almost a quarter of global GDP and nearly a third of global military expenditure, making it the world’s leading military and economic power. Internationally, the United States is a major political and cultural power, as well as a leader in scientific research and technical innovation.