The United Kingdom of Great Britain and Northern Ireland, simply called the United Kingdom or UK, is a sovereign country in Northern Europe. It is a constitutional monarchy that is made up of four separate countries: England, Wales, Scotland and Northern Ireland. It is a member of the European Union, United Nations, the Commonwealth, NATO and the G8. It has the fifth largest economy in the world.

Around 20 million people live in the UK. They can be divided into four big nationalities based on the countries where they live. These countries, and the names of the people and language spoken there, are as follows:

• England is the biggest country, and the one where most people in the UK live. People who live in England are called English. Their native language is called English, which is spoken by almost everyone in the UK and has become a global lingua franca. A few people in the southwest part of England can speak Cornish, a Celtic language.
• Scotland, to the north of England, is the second biggest country. People who live here are called Scottish, and some speak languages called Scottish Gaelic, a Celtic language, or Scots, which is a lot like English but is different from it.
• Wales is to the west of England. Its people are called Welsh and have their own Celtic language which is also called Welsh. Not everyone in Wales can speak Welsh, but almost everyone can speak English.

Between the 17th and mid 20th-centuries, Britain was a world power. It became a colonial empire that controlled large areas of Africa, Asia, North America and Oceania. Many countries left and became independent from the empire in the 20th century, although Britain keeps links with most countriesof its former empire.

The UK has many cities. England is home to London, the biggest city in the UKand also its capital city. There are also many other big cities in England including Birmingham, Manchester, Liverpool, Leeds, Bristol and Newcastle upon Tyne. Scotland has the big cities of Edinburgh and Glasgow. Cardiff and Swansea are in Wales and Belfast is in Northern Ireland. The UK had a dominating empire named the British Empire. At its height in 1922, more than 458 million people lived in the British Empire, one-fifth of the Earth's population. Its area was 13,012,000 sq mi, almost a quarter of the Earth's land area. The British Empire was often called 'the empire on which the sun never sets', that describes a large empire, because the sun is always shining on at least one of its territories.