United States (Global Catastrophe)

The United States of America (USA), commonly known as the United States (U.S.) or America, is a constitutional democratic federal republic composed of 53 states, three major self-governing territories, and various possession scattered across the world. 48 states and the federal district are located in North America, while the rest of the states are scattered across the Pacific and the Caribbean. The United States has extremely diverse geography, climate, and wildlife, making it one of the world's megadiverse countries.

At 3.8 million square miles (9.8 million km2) and with a population of over 500 million people, the United States is the world's fifth-largest nation by land area, and the fourth-most populous nation in the world. The nation's capital is the city of Washington, located in the state of Potomac, and the largest city is the city of New York, located in the state of New York.

Paleo-Indians migrated from Asia to North American via the Bering land bridge at least 15,000 years ago, and European colonization of the continent began in the 16th century. The United States emerged from 13 British colonies along what is now the nation's east coast in the late 18th century following the American Revolution. The nation's current constitution was adopted in 1788, but has been amended over 50 times since.

The United States embarked on a vigorous expansion across the continent in the 19th century, and spanned from the Atlantic to the Pacific by 1848. As the century drew to a close, the American Civil War re-affirmed national unity and led to the end of legal slavery in the country, and driven by the Industrial Revolution, the American economy began to soar, eventually becoming the largest economy in the world.

The Spanish-American War and World War I established the nation's status as a global military power, and it emerged from World War II as a superpower. The Cold War, an ideological and political conflict between the United States and the Soviet Union, dominated most of the 20th century, ending with the fall of the Soviet Union in late 1991. For several decades after, the nation was the world's sole superpower, but its dominance was eventually replaced by other nations such as China, India, Brazil, Argentina, and Indonesia as the 21st century continued. The United States remains a player in world affairs, but is no longer considered to be a superpower.