The United Kingdom of Great Britain and Northern Ireland (usually shortened to the United Kingdom, the U.K., or Britain is a country and sovereign state to the northwest of mainland Europe. It comprises the island of Great Britain, the north-east part of the island of Ireland and many small local islands. Northern Ireland is the only part of the UK with a land border, sharing it with the Republic of Ireland Apart from this land border, the UK is surrounded by the waters of the Atlantic Ocean, the North Sea, the English Channel, and the Irish Sea. It is linked to France by the Channel Tunnel.

The United Kingdom is a constitutional monarchy comprising four constituent countries: England, Northern Ireland, Scotland and Wales. The current monarch is Queen Elizabeth II who is also Queen and Head of State of fifteen other Commonwealth Realms including Canada, Australia, New Zealand and Jamaica. The Crown Dependencies of the Channel Islands and the Isle of Man, formally possessions of the Crown, are not part of the UK but form a federacy with it. The UK has fourteen overseas territories, all remnants of the British Empire, which at its height encompassed almost a quarter of the world's land surface.

Britain was the world's foremost power during the 19th and early 20th century, the economic cost of two world wars and the decline of its empire in the latter half of the 20th century diminished Britain's role and status in global affairs. The UK remains an important political, economic and nuclear military power; it holds a permanent seat on the United Nations Security Council and is a member of the G8, NATO, the European Union and the Commonwealth of Nations

England and Scotland had existed as separate sovereign and independent states with their own monarchs and political structures since the 9th century. The once independent Principality of Wales fell under the control of English monarchs from the Statute of Rhuddlan in 1284. Under the Acts of Union 1707, England (including Wales) and Scotland, which had been in personal union since the Union of the Crowns in 1603, agreed to a political union in the form of a unified Kingdom of Great Britain. The Act of Union 1800 united the Kingdom of Great Britain with the Kingdom of Ireland, which had been gradually brought under English control between 1541 and 1691, to form the United Kingdom of Great Britain and Ireland in 1801Independence for the Republic of Ireland in 1922 followed the partition of the island of Ireland two years previously, with six of the nine counties of the province of Ulster remaining within the UK, which then changed to the current name in 1927 of the United Kingdom of Great Britain and Northern Ireland

Britain was an important part of the Age of Enlightenment with philosophical and scientific input and a literary and theatrical tradition.Over the next century the United Kingdom played an important role in developing Western ideas of parliamentary democracy with significant contributions to literature, the arts and science The wealth of the British Empire, like other Great Powers, was also partly generated by colonial exploitation, including the industrialisation after 1750 of the slave trade, with Britain's 18th century shipping fleet, the largest in the world, taking African slaves to the Americas as part of the infamous triangular trade. At the beginning of the 19th however, Britain passed the Slave Trade Act and became the first nation to permanently prohibit trade in slaves.

The British Empire in 1897. The largest in history, the British Empire led to the current spread of the English languageAfter the Industrial Revolution and the defeat of Napoleon in the Napoleonic Wars, Britain became the principal naval power of the 19th century. At its peak, the British Empire, which is considered to be both the United Kingdom and areas that are legally separate entities from, but controlled by, the UK, composed of large territories in Asia, Africa and America.

Over the 19th century the country played an important role in the development of parliamentary democracy, partly via the emergence of a multi-party system. Developments of science and the arts, building on an 18th century inheritance of figures such as Isaac Newton, and particularly its earlier tradition of literature, were influential. At the end of the Victorian era, however, the United Kingdom lost its industrial leadership, particularly to the United States, which surpassed the UK in industrial production and trade in the 1890s, as well as to the German Empire. Britain remained an eminent power, and its empire expanded to its maximum size by 1921, gaining the League of Nations mandate over former German and Ottoman colonies after World War I.

After emergence from the war, the world's first large-scale international broadcasting network, the BBC, was created. The country's Labour movement had been in expansion since the late 19th century, and in 1924 the first Labour government came to power. Britain fought Nazi Germany in World War II, with its Commonwealth allies including Canada, Australia, New Zealand, South Africa and India, later to be joined by further allies. Wartime leader Winston Churchill and his successor Clement Atlee helped plan the post-war world as part of the "Big Three". World War II, however, left the United Kingdom financially and physically damaged. Economically costly wartime loans, loans taken in 1945 from the United States and from Canada, combined with post-war Marshall Plan aid from the United States started the United Kingdom on the road to recovery.

The famous Spitfire of the RAF in World War II.1945 saw the emergence of the British Welfare State and one of the world's first and most comprehensive Health Services, while the demands of a recovering economy brought people from all over the Commonwealth to create a multiethnic Britain. Although the new postwar limits of Britain's political role were confirmed by the Suez Crisis of 1956, the international currency of the language meant the continuing impact of its literature and culture, while at the same time from the 1960s its popular culture found an influence abroad. Following a period of economic stagnation and industrial strife in the 1970s after a global economic downturn, the 1980s saw the premiership of Margaret Thatcher, under whom a marked break with the post-war political and economic consensus saw, for her supporters, economic recovery, and, for her critics, greater social division. From the mid-1990s onward these trends largely continued under the leadership of Tony Blair.

The United Kingdom has been a member of the European Union since 1973. The attitude of the present Labour government towards further integration with this organisation is mixed,[18] with the Conservative Party favouring a return of some powers and competencies to the state, and the Liberal Democrats supportive of current engagement.

Administrative subdivisions
England | Scotland | Wales | Northern Ireland