The United Kingdom of Great Britain and Northern Ireland (usually shortened to the United Kingdom, the UK, or Britain)[6] is a sovereign state that lies to the north-west of Continental Europe with the Republic of Ireland to the west. It occupies all of the island of Great Britain and the north-east part of the island of Ireland, sharing a land border with the Republic of Ireland.
The United Kingdom is bounded by the Atlantic Ocean, and its ancillary bodies of water, including the North Sea, the English Channel, the Celtic Sea, St George's Channel, and the Irish Sea. The United Kingdom is linked to France by the Channel Tunnel.
The United Kingdom is a constitutional monarchy composed of four constituent countries: England, Scotland, Wales and Northern Ireland. The current monarch is Queen Elizabeth II, who is also the Queen and Head of State of fifteen other Commonwealth Realms, including Canada, Australia, New Zealand and Jamaica. The dependencies of the Channel Islands and the Isle of Man, formally possessions of the Crown, form a federacy with the United Kingdom collectively known as the British Islands. The UK also has fourteen[7] overseas territories, including Bermuda, Gibraltar, Pitcairn Islands, the British Indian Ocean Territory, and the Falkland Islands, remnants of the British Empire, which was at its height the world's most extensive empire.
Although Britain was the world's foremost great power during the 18th and 19th centuries, the economic cost of two world wars and the decline of its empire in the latter half of the 20th century diminished Britain's status in global affairs. However, as a permanent member of the Security Council, a nuclear power, a member of the G8 and the fifth largest economy in the world, Britain remains a strong military and economic power.