The United Kingdom of Great Britain and Northern Ireland (commonly known as the United Kingdom, the UK or Britain) is a sovereign state located off the north-western coast of continental Europe. The country includes the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands. Northern Ireland is the only part of the UK that shares a land border with another sovereign state—the Republic of Ireland. Apart from this land border the UK is surrounded by the Atlantic Ocean, the North Sea, the English Channel and the Irish Sea.
The total area of the United Kingdom is approximately 243,610 square kilometers (94,060 sq mi). The country occupies the major part of the British Isles archipelago and includes the island of Great Britain, the north-eastern one-sixth of the island of Ireland and some smaller surrounding islands. It lies between the North Atlantic Ocean and the North Sea with the south-east coast coming within 35 kilometers (22 mi) of the coast of northern France, from which it is separated by the English Channel. As of 1993 10% of the UK was forested, 46% used for pastures and 25% used for agriculture. The Royal Greenwich Observatory in London is the defining point of the Prime Meridian.
The main rivers and estuaries are the Thames, Severn and the Humber.
The history of the British Isles has witnessed intermittent periods of competition and cooperation between the people that occupy the various parts of Great Britain, Ireland, and the smaller adjacent islands, which together make up the British Isles, as well as with France, Germany, the Low Countries, Denmark, Scandinavia, etc.
Today, the British Isles contain two sovereign states: the Republic of Ireland and the United Kingdom. There are also three Crown dependencies: Guernsey, Jersey and the Isle of Man. The United Kingdom may be further broken down into the four countries of the United Kingdom: England, Northern Ireland, Scotland, and Wales. Each of these countries bears its own history, with all but Northern Ireland having been independent states at one point. The History of the formation of the United Kingdom is very complex.
The British monarch was head of state of all of the countries of the British Isles from the Union of the Crowns in 1603 until the enactment of the Republic of Ireland Act in 1949, although the term "British Isles" was not used in 1603. Additionally, since the independence of Ireland, historians of the region often avoid the term British Isles due to the complexity of relations between the peoples of the archipelago.