A country of western Europe consisting of England, Wales, Scotland, and Northern Ireland; population 64,700,000 (estimated 2015); capital, London. Full name United Kingdom of Great Britain and Northern Ireland.
England (which had incorporated Wales in the 16th century) and Scotland have had the same monarch since 1603, when James VI of Scotland succeeded to the English crown as James I; the kingdoms were formally united by the Act of Union in 1707. An Act of Parliament joined Great Britain and Ireland in 1801, but the Irish Free State (later the Republic of Ireland) broke away in 1921. The UK became a member of the European Community (now the EU) in 1973; in 2016 it voted to leave the EU, and it left in 2020