The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain /ˈbrɪ.tən/, is a sovereign state located off the northwestern coast of continental Europe. The country includes the island of Great Britain (a term sometimes also loosely applied to the whole state), the northeastern part of the island of Ireland, and many smaller islands. Northern Ireland is the only part of the UK that shares a land border with another state: the Republic of Ireland. Apart from this land border, the UK is surrounded by the Atlantic Ocean, with the North Sea in the east and the English Channel in the south; the Irish Sea separates Great Britain from Ireland. The UK has an area of 243,610 square kilometres (94,060 sq mi), making it the 78th largest sovereign state in the world and the 11th largest in Europe.
The United Kingdom is the 22nd most populous country, with an estimated 64.1 million inhabitants. It is a constitutional monarchy and has a parliamentary system of governance. Its capital city is London, an important global city and financial centre with the second-largest urban area in the European Union. The current British monarch—since 6 February 1952—is Queen Elizabeth II. The UK consists of four countries: England, Scotland, Wales and Northern Ireland. The latter three have devolved administrations, each with varying powers, based in their capitals, Edinburgh, Cardiff and Belfast, respectively. Guernsey, Jersey and the Isle of Man are not part of the United Kingdom, being Crown dependencies with the British Government responsible for defence and international representation. The United Kingdom has fourteen Overseas Territories, including the disputed Falkland Islands and Gibraltar.
The relationships among the countries of the United Kingdom have changed over time. The Principality of Wales was incorporated into the Kingdom of England in 1536. In 1707, the kingdoms of Scotland and England were united to form the Kingdom of Great Britain, which in 1801, united with the Kingdom of Ireland to form the United Kingdom of Great Britain and Ireland. In 1922, five-sixths of Ireland seceded from the UK, leaving the present formulation of the United Kingdom of Great Britain and Northern Ireland. British Overseas Territories, formerly colonies, are the remnants of the British Empire which, at its height in the late 19th and early 20th centuries, encompassed almost a quarter of the world's land mass and was the largest empire in history. British influence can be observed in the language, culture and legal systems of many of its former colonies.
The United Kingdom is a developed country and has the world's sixth-largest economy by nominal GDP and eighth-largest by purchasing power parity. It was the world's first industrialised country and the world's foremost power during the 19th and early 20th centuries. The UK remains a great power with considerable economic, cultural, military, scientific and political influence internationally. It is a recognised nuclear weapons state and its military expenditure ranks from fourth to sixth (depending on the source) in the world. The UK has been a permanent member of the United Nations Security Council since its first session in 1946. It has been a member of the European Union (EU) and its predecessor the European Economic Community (EEC) since 1973; it is also a member of the Commonwealth of Nations, the Council of Europe, the G7, the G8, the G20, NATO, the Organisation for Economic Co-operation and Development (OECD) and the World Trade Organization (WTO).