The United Kingdom, officially the United Kingdom of Great Britain and Northern Ireland, is a sovereign state off the north-western coast of continental Europe. The largest island nation in Europe is a union of four countries, the formerly independent individual states England, Scotland, Wales and the northeastern part of the island of Ireland and many smaller islands. The archipelago is surrounded by the Atlantic Ocean, the North Sea, the English Channel, and the Irish Sea. Further, the UK has three Crown Dependencies and fifteen overseas territories. The United Kingdom is a unitary state governed under a constitutional monarchy and a parliamentary system, with the British monarch as head of state.