The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a sovereign state and country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. The United Kingdom includes the island of Great Britain, the north-eastern part of the island of Ireland, and many smaller islands within the British Isles. Northern Ireland shares a land border with the Republic of Ireland; otherwise, the United Kingdom is surrounded by the Atlantic Ocean, the North Sea, the English Channel, the Celtic Sea and the Irish Sea. The total area of the United Kingdom is , with an estimated 2020 population of more than 67 million people. The United Kingdom has evolved from a series of annexations, unions and separations of constituent countries over several hundred years. The Treaty of Union between the Kingdom of England (which included Wales, annexed in 1542) and the Kingdom of Scotland in 1707 formed the Kingdom of Great Britain. Its union in 1801 with the Kingdom of Ireland created the United Kingdom of Great Britain and Ireland. Most of Ireland seceded from the UK in 1922, leaving the present United Kingdom of Great Britain and Northern Ireland, which formally adopted that name in 1927. The nearby Isle of Man, Guernsey and Jersey are not part of the UK, being Crown Dependencies, but the British Government is responsible for their defence and international representation. There are also 14 British Overseas Territories, the last remnants of the British Empire which, at its height in the 1920s, encompassed almost a quarter of the world's landmass and a third of the world's population, and was the largest empire in history. British influence can be observed in the language, culture and the legal and political systems of many of its former colonies. The United Kingdom is a constitutional monarchy and parliamentary democracy. The capital and largest city is London, a global city and financial centre with a metropolitan area population of over 14 million. Other major cities include Birmingham, Liverpool, Sheffield, Bristol and Glasgow. Scotland, Wales, and Northern Ireland have their own devolved governments, each with varying powers. The UK became the world's first industrialised country and was the world's foremost power during the 19th and early 20th centuries, during a period of unchallenged global hegemony known as "Pax Britannica". In the 21st century, the