It has a high-income economy and a very high human development index rating, ranking 14th in the world. It was the world's first industrialised country and the world's foremost power during the 19th and early 20th centuries. The UK remains a great power, with considerable economic, cultural, military, scientific and political influence internationally. It is a recognised nuclear weapons state and is sixth in military expenditure in the world. It has been a permanent member of the United Nations Security Council since its first session in 1946. The United Kingdom is a leading member of the Commonwealth of Nations, the Council of Europe, the G7, the G20, NATO, the Organisation for Economic Co-operation and Development (OECD), Interpol and the World Trade Organization (WTO). It was a member of the European Union (EU) and its predecessor, the European Economic Community (EEC) for 47 years, between 1 January 1973 and withdrawal on 31 January 2020. The 1707 Acts of Union declared that the kingdoms of England and Scotland were "United into One Kingdom by the Name of Great Britain". The term "United Kingdom" has occasionally been used as a description for the former kingdom of Great Britain, although its official name from 1707 to 1800 was simply "Great Britain". The Acts of Union 1800 united the kingdom of Great Britain and the kingdom of Ireland in 1801, forming the United Kingdom of Great Britain and Ireland. Following the partition of Ireland and the independence of the Irish Free State in 1922, which left Northern Ireland as the only part of the island of Ireland within the United Kingdom, the name was changed to the "United Kingdom of Great Britain and Northern Ireland". Although the United Kingdom is a sovereign country, England, Scotland, Wales and Northern Ireland are also widely referred to as countries. The UK Prime Minister's website has used the phrase "countries within a country" to describe the United Kingdom. Some statistical summaries, such as those for the twelve NUTS 1 regions of the United Kingdom refer to Scotland, Wales and Northern Ireland as "regions". Northern Ireland is also referred to as a "province". With regard to Northern Ireland, the descriptive name used "can be controversial, with the choice often revealing one's political preferences". The term "Great Britain" conventionally refers to the island of Great Britain, or politically to England, Scotland and Wales in combination. It is sometimes used as a loose synonym for the United Kingdom as a whole. The term "Britain" is used both as a synonym for Great Britain, and as a synonym for the United Kingdom.