The U.S. is a country of 50 states covering a vast swath of North America, with Alaska in the northwest and Hawaii extending the nation's presence into the Pacific Ocean. Major Atlantic Coast cities are New York, a global finance and culture center, and capital Washington, DC. Midwestern metropolis Chicago is known for influential architecture and on the west coast, Los Angeles' Hollywood is famed for filmmaking.
At 3.8 million square miles (9.8 million km2) and with over 324 million people, the United States is the world's third- or fourth-largest country by total area, 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.
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 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 to develop nuclear weapons, the only country to use them in warfare, and a permanent member of the United Nations Security Council.