The United States, officially the United States of America, is a sovereign country constituted as a federal constitutional republic composed of fifty states and a federal district. Most of the country is located in the middle of North America -where its forty-eight contiguous states meet and Washington DC, the federal district-, between the Pacific and Atlantic Oceans, borders Canada to the north and Mexico to the south. The state of Alaska is in the northwest of the continent, bordering Canada to the east, separated from Russia to the west by the Bering Strait. The state of Hawaii is a Polynesian archipelago in the middle of the Pacific Ocean, and is the only one of its states that is not found in America.
The country has several unincorporated territories in the Caribbean Sea and the Pacific. With 9.83 million km², and with more than 325 million inhabitants, the country is the fourth largest in total area, the fifth largest in contiguous area and the third largest in population. It is one of the most ethnically diverse and multicultural nations, a product of large-scale immigration, the largest national economy in the world in nominal terms, with an estimated GDP of 15.7 billion dollars and a fifth of the Global GDP in purchasing power parity. The country is the main capitalist force on the planet, as well as being a leader in scientific research and technological innovation since the 19th century and, since the beginning of the 20th century, the main industrial country.
With high levels enjoyed by many public and private institutions of competitive higher education under open admission policies. In GDP PPA, EE. UU It is the second largest economy, behind the People's Republic of China. The Amerindian peoples have inhabited what is the continental territory of the United States for thousands of years. This Amerindian population was reduced by disease and war after the first contact with Europeans. The United States was founded by thirteen British colonies, along the Atlantic coast. On July 4,1776, they issued the Declaration of Independence, which proclaimed their right to self-determination and the establishment of a cooperative union. The rebel states defeated the British Empire in the war of independence, the first successful colonial war of independence. The Constitution of the United States was adopted on September 17,1787.
Its ratification the following year made the states part of a single republic with a strong central government. The Bill of Rights, which comprises ten constitutional amendments guaranteeing many fundamental civil rights and freedoms, was ratified in 1791. In the 19th century, the United States acquired territories from France, Spain, the United Kingdom, Mexico, Russia and Japan, as well as to annex the republics of Florida, Texas, California and Hawaii. In the 1860s, disputes between the agrarian and conservative south and the industrial and progressive north over the rights of states and the abolition of slavery led to the Civil War. The victory of the north prevented a permanent division of the country and led to the end of legal slavery.
By the 1890s, the national economy was the largest in the world and the Spanish-American War and the First World War confirmed its status as a military power. After the Second World War, it emerged as the first country with nuclear weapons and a permanent member of the Security Council of the United Nations. The end of the Cold War and the dissolution of the Soviet Union left it as the only international superpower. The country represents two fifths of the world military expenditure and is a leading economic, political and cultural force in the world.