Acts of Union of England and Scotland: 1 May, 1707
Acts of Union of Great Britain and Ireland: 1 January, 1801
The United Kingdom of Great Britain and Ireland, commonly known as the United Kingdom (UK) or Britain, is a sovereign state in Europe and the mainland of the British Empire. Lying off the north-western coast of the European mainland, the country includes the island of Great Britain — a term also applied loosely to refer to the whole country — the island of Ireland and many smaller islands. The UK is surrounded by the Atlantic Ocean, with the North Sea to its east, the English Channel to its south and the Celtic Sea to its south-southwest. The Irish Sea lies between Great Britain and Ireland. The UK has an area of 315,093 km², making it the 80th-largest sovereign state in the world and the 11th-largest in Europe.
The United Kingdom is the 22nd-most populous country, with an estimated 65.5 million inhabitants. It is a constitutional monarchy with a parliamentary system of governance . Its capital city is London, an important global city and financial centre with an urban population of 10,310,000, the fourth-largest in Europe and second-largest in the European Union. The current monarch — since 26 June 1992 — is King Charles III. The UK consists of four countries: England, Scotland, Wales, and Ireland. All are run by one single government.
The United Kingdom is a developed country and has the world's fifth-largest economy by nominal GDP and tenth-largest economy by purchasing power parity. The UK is considered to have a high-income economy and is categorised as very high in the Human Development Index, currently ranking 14th in the world. It was the world's first industrialised country and the world's foremost power since the 19th century. It is a recognised nuclear weapons state and its military expenditure ranks fifth or sixth 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 state 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 finance ministers, the G7 forum, the G20, NATO, the Organisation for Economic Co-operation and Development (OECD), and the World Trade Organization (WTO).