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. 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 square miles: almost a quarter of the Earth's land area. The empire was sometimes called 'the empire on which the sun never sets', meaning the sun is always shining on at least one of its territories. Almost all countries left and became independent from the empire in the 20th century, although Britain keeps links with most countries of its former empire.