The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a transcontinental country located primarily in North America. It consists of 50 states, a federal district, five major unincorporated territories, nine minor outlying islands, and 326 Indian reservations. It is the third-largest country by total area.[d] The United States shares land borders with Canada to its north and with Mexico to its south. It has maritime borders with the Bahamas, Cuba, Russia, and other nations.[k] With a population of over 331 million, it is the third most populous country in the world. The national capital is Washington, D.C., and the most populous city and financial center is New York City.

By 1900, the United States had become the world's largest economy, and the Spanish–American War and World War I established the country as a world power. After Japan's surprise attack on Pearl Harbor in 1941, the U.S. entered World War II on the Allied side. The aftermath of the war left the United States and the Soviet Union as the world's two superpowers. During the Cold War, both countries engaged in a struggle for ideological dominance but avoided direct military conflict. They also competed in the Space Race, which culminated in the 1969 American spaceflight that first landed humans on the Moon. Simultaneously, the civil rights movement led to legislation abolishing state and local Jim Crow laws and other codified racial discrimination against African Americans. The Soviet Union's dissolution in 1991 ended the Cold War, leaving the United States as the world's sole superpower. The September 11 attacks in 2001 resulted in the United States launching the war on terror, which included the War in Afghanistan (2001–2021) and the Iraq War (2003–2011).

The United States is a federal republic with three separate branches of government, including a bicameral legislature. It is a liberal democracy and market economy; it ranks high in international measures of human rights, quality of life, income and wealth, economic competitiveness, and education; and it has low levels of perceived corruption. It has high levels of incarceration and inequality, allows capital punishment, and lacks universal health care. As a melting pot of cultures and ethnicities, the U.S. has been shaped by centuries of immigration. It has a highly diverse climate and geography and is officially recognized as one of the 17 ecologically megadiverse countries.

Reference - https://en.wikipedia.org/wiki/United_States