The United Kingdom of Great Britain and Northern Ireland,commonly known as the United Kingdom (UK) or simply Britain /ˈbrɪ.tən/, is a sovereign state located off the northwestern coast of continental Europe. The country includes the island of Great Britain (a term sometimes also loosely applied to the whole state), the northeastern 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 state: the Republic of Ireland. Apart from this land border, the UK is surrounded by the Atlantic Ocean, with the North Sea in the east, the English Channel in the south and the Irish Sea in the west.
The relationships among the countries of the United Kingdom have changed many times. The Principality of Wales was joined to England in 1536, forming the Kingdom of England. In 1707, the kingdoms of Scotland and England were united to form the Kingdom of Great Britain. In 1801, the Irish and British parliaments were combined to form the United Kingdom of Great Britain and Ireland. In 1922, five-sixths of Ireland left the UK to form the Irish Free State, leaving the present formulation of the United Kingdom of Great Britain and Northern Ireland.