The United Kingdom has the sixth-largest national economy in the world (and third-largest in Europe) measured by nominal GDP and eighth-largest in the world (and second-largest in Europe) measured by purchasing power parity (PPP). The UK's GDP per capita is the 22nd-highest in the world in nominal terms and 22nd-highest measured by PPP. In 2012, the UK was the 11th-largest exporter in the world and the sixth-largest importer. In 2012 the UK had the third-largest stock of inward foreign direct investment and the second-largest stock of outward foreign direct investment. The British economy comprises (in descending order of size) the economies of England, Scotland, Wales and Northern Ireland. The UK has one of the world's most globalised economies.
The service sector dominates the UK economy, contributing around 78% of GDP, with the financial services industry particularly important. London is the world's largest financial centre alongside New York and has the largest city GDP in Europe. The UK aerospace industry is the second- or third-largest national aerospace industry depending on the method of measurement. The pharmaceutical industry plays an important role in the economy and the UK has the third-highest share of global pharmaceutical R&D. The automotive industry is also a major employer and exporter. The British economy is boosted by North Sea oil and gas production; its reserves were valued at an estimated £250 billion in 2007. There are significant regional variations in prosperity, with the South East of England and southern Scotland the richest areas per capita.
The United States of America (USA), commonly referred to as the United States (US), America, or simply the States, is a federal republic consisting of 50 states, 16 territories, and a federal district. The 48 contiguous states and the federal district of Washington, D.C., are in central North America between Canada and Mexico. The state of Alaska is the northwestern part of North America and the state of Hawaii is an archipelago in the mid-Pacific. The country also has five populated and nine unpopulated territories in the Pacific and the Caribbean. The largest of these territories are Puerto Rico and the American Virgin Islands which are an official part of the United States. At 3.79 million square miles (9.83 million km2) in total and with around 316 million people, the United States is the fourth-largest country by total area and third largest by population. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The geography and climate of the United States is also extremely diverse, and it is home to a wide variety of wildlife.
Paleo-indians migrated from Asia to what is now the U.S. mainland around 15,000 years ago, with European colonization beginning in the 16th century. The United States emerged from 13 British colonies located along the Atlantic seaboard. Disputes between Great Britain and these colonies led to the American Revolution. On July 4, 1776, delegates from the 13 colonies unanimously issued the Declaration of Independence. The ensuing war ended in 1783 with the recognition of independence of the United States from the Kingdom of Great Britain, and was the first successful war of independence against a European colonial empire. The current Constitution was adopted on September 17, 1787. The first 10 amendments, collectively named the Bill of Rights, were ratified in 1791 and guarantee many fundamental civil rights and freedoms.