United Kingdom
The United Kingdom of Great Britain and Northern Ireland (UK) comprises the countries of England, Scotland, Wales, and Northern Ireland. It is a Nation State. The Channel Islands and the Isle of Man are not part of the United Kingdom, but are within The British Isles, and are included in this Wiki for convenience. "Great Britain" is the largest island within the British Isles, but is a term often used interchangeably with The United Kingdom.
London is the capital city of England and is where the government of the UK is situated. The countries of Wales and Scotland have devolved governments, giving them certain powers that affect their regional governance. Cardiff's assembly is in the Welsh capital city of Cardiff, Scotland's government is located in Hollyrood.
History
Historically, England, Ireland, and Scotland were three separate countries. From early mediaeval times the Kings of England were Lords, and later Kings, of Ireland, but Scotland had its own Kings and Queens. When James VI of Scotland became King of England (as James I) in 1603 the two crowns were united, but Scotland retained its separate govenment until it was united with England to form the Kingdom of Great Britain in 1707, under Queen Anne. A further union (in which Lord Castlereagh took a leading role) happened in 1801, forming the United Kingdom of Great Britain and Ireland. This lasted until Ireland was partitioned in 1922, after which it has been the United Kingdom of Great Britain and Northern Ireland.