Which was the largest empire in history?

An empire involves the extension of a state's sovereignty over external territories and a variety of different ethnic groups. The term "empire" in this context (not necessarily a state ruled by an emperor) does not have a precise definition, but is generally applied to political entities that are considered to be especially large by the standards of their time and that have acquired a significant part of their territory by conquest.

The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom and its predecessor states. It originated with the overseas possessions and trading posts established by England between the late 16th and early 18th centuries. At its height, it was the largest empire in history and, for over a century, was the foremost global power. By 1913, the British Empire held sway over 412 million people, 23% of the world population at the time, and by 1920, it covered 35,500,000 km2 (13,700,000 sq mi), 24% of the Earth's total land area. As a result, its political, legal, linguistic and cultural legacy is widespread. At the peak of its power, the phrase "the empire on which the sun never sets" was often used to describe the British Empire, because its expanse around the globe meant that the sun was always shining on at least one of its territories.