<P> The United Kingdom is a constitutional monarchy with a parliamentary democracy . The monarch is Queen Elizabeth II, who has reigned since 6 February 1952 . The capital of the United Kingdom and its largest city is London, a global city and financial centre with an urban area population of 10.3 million, the fourth - largest in Europe and second - largest in the European Union . Other major urban areas in the United Kingdom include the conurbations centred on Birmingham, Leeds, Glasgow, Liverpool and Manchester . The United Kingdom consists of four countries--England, Scotland, Wales and Northern Ireland . The last three have devolved administrations, each with varying powers, based in their capitals, Edinburgh, Cardiff and Belfast, respectively . The nearby Isle of Man, Bailiwick of Guernsey and Bailiwick of Jersey are not part of the United Kingdom, being Crown dependencies with the British Government responsible for defence and international representation . </P> <P> Prior to the creation of the United Kingdom, Wales was conquered and annexed by the Kingdom of England . This meant that the Treaty of Union between England and Scotland resulted in the birth of a single, united kingdom encompassing all of Great Britain, coming into being in 1707 . The Kingdom of Ireland then merged with this state in 1801 to form the United Kingdom of Great Britain and Ireland . Five - sixths of Ireland seceded from the UK in 1922, leaving the present formulation of the United Kingdom of Great Britain and Northern Ireland . There are fourteen British Overseas Territories . These are the remnants of the British Empire which, at its height in the 1920s, 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 . </P> <P> The United Kingdom is a developed country and has the world's fifth - largest economy by nominal GDP and ninth - 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, ranking 16th in the world . 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 is seventh in military expenditure 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 leading member state of the EU and its predecessor, the European Economic Community (EEC), since 1973 . However, on 23 June 2016, a national referendum on the UK's membership of the EU resulted in a decision to leave, and its exit from the EU is currently being negotiated . The UK 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). </P> <P> The 1707 Acts of Union declared that the kingdoms of England and Scotland were "United into One Kingdom by the Name of Great Britain", though the new state is also referred to in the Acts as the "Kingdom of Great Britain", "United Kingdom of Great Britain" and "United Kingdom". The term "United Kingdom" is found in informal use during the 18th century and the country was also occasionally referred to as the "United Kingdom of Great Britain" though its full official name, from 1707 to 1800, was merely "Great Britain", without a "long form". The Acts of Union 1800 united the Kingdom of Great Britain and the Kingdom of Ireland in 1801, forming the United Kingdom of Great Britain and Ireland . Following the partition of Ireland and the independence of the Irish Free State in 1922, which left Northern Ireland as the only part of the island of Ireland within the United Kingdom, the name "United Kingdom of Great Britain and Northern Ireland" was adopted . </P>

Is it united kingdom or the united kingdom