Undid revision 1233639601 by JJpeterson (talk): The source does not specify military power, and there are other kinds (in particular, overall power may be a function of several different kinds in combination).
[[File:Combined_map_-_British_and_Mongol_Empires.svg|upright=1.5|alt=A map of the British and Mongol empires at their respective greatest extents|thumb|The [[British Empire]] (red) and [[Mongol Empire]] (blue) were the largest and second-largest empires in history, respectively. The precise extent of the Mongol Empire at its greatest territorial expansion is a matter of debate among scholars.]]
Several [[empire]]s in [[human history]] have been contenders for the largest of all time, depending on definition and mode of measurement. Possible ways of measuring size include area, population, economy, and military power. Of these, area is the most commonly used because it has a fairly precise definition and can be feasibly measured with some degree of accuracy.<ref>{{Cite journal|last=Taagepera|first=Rein|author-link=Rein Taagepera|date=1978|title=Size and duration of empires: Systematics of size|url=https://escholarship.org/content/qt8vx325vq/qt8vx325vq_noSplash_a2c2db5cdb06a3d4d4e35b2852a74948.pdf|url-status=live|journal=[[Social Science Research]]|language=en|volume=7|issue=2|pages=111|doi=10.1016/0049-089X(78)90007-8|issn=0049-089X|archive-url=https://web.archive.org/web/20200707192527/https://escholarship.org/content/qt8vx325vq/qt8vx325vq_noSplash_a2c2db5cdb06a3d4d4e35b2852a74948.pdf|archive-date=2020-07-07|access-date=2020-07-07}}</ref> Estonian political scientist [[Rein Taagepera]], who published a series of academic articles about the territorial extents of historical empires between 1978 and 1997,<ref>{{Cite journal|last=Taagepera|first=Rein|author-link=Rein Taagepera|date=1978|title=Size and duration of empires: Systematics of size|url=https://escholarship.org/content/qt8vx325vq/qt8vx325vq_noSplash_a2c2db5cdb06a3d4d4e35b2852a74948.pdf|url-status=live|journal=[[Social Science Research]]|language=en|volume=7|issue=2|pages=108–127|doi=10.1016/0049-089X(78)90007-8|issn=0049-089X|archive-url=https://web.archive.org/web/20200707192527/https://escholarship.org/content/qt8vx325vq/qt8vx325vq_noSplash_a2c2db5cdb06a3d4d4e35b2852a74948.pdf|archive-date=2020-07-07|access-date=2020-07-07}}</ref><ref>{{Cite journal|last=Taagepera|first=Rein|author-link=Rein Taagepera|date=1978|title=Size and Duration of Empires: Growth-Decline Curves, 3000 to 600 B.C.|url=https://escholarship.org/content/qt6wf6m5qg/qt6wf6m5qg.pdf|url-status=live|journal=[[Social Science Research]]|volume=7|issue=2|pages=180–196|doi=10.1016/0049-089x(78)90010-8|issn=0049-089X|archive-url=https://web.archive.org/web/20200707202816/https://escholarship.org/content/qt6wf6m5qg/qt6wf6m5qg.pdf|archive-date=2020-07-07|access-date=2020-07-07}}</ref><ref>{{cite journal|last1=Taagepera|first1=Rein|author-link=Rein Taagepera|date=1979|title=Size and Duration of Empires: Growth-Decline Curves, 600 B.C. to 600 A.D.|journal=[[Social Science History]]|volume=3|issue=3/4|pages=115–138|doi=10.2307/1170959|jstor=1170959}}</ref><ref>{{cite journal|author=Taagepera|first=Rein|author-link=Rein Taagepera|date=September 1997|title=Expansion and Contraction Patterns of Large Polities: Context for Russia|url=https://escholarship.org/content/qt3cn68807/qt3cn68807.pdf|url-status=live|journal=[[International Studies Quarterly]]|volume=41|issue=3|pages=475–504|doi=10.1111/0020-8833.00053|jstor=2600793|archive-url=https://web.archive.org/web/20200707203055/https://escholarship.org/content/qt3cn68807/qt3cn68807.pdf|archive-date=2020-07-07|access-date=2020-07-07}}</ref> defined an empire as "any relatively large sovereign political entity whose components are not sovereign" and its size as the area over which the empire has some undisputed military and taxation prerogatives.<ref>{{cite journal|last1=Taagepera|first1=Rein|author-link=Rein Taagepera|date=1979|title=Size and Duration of Empires: Growth-Decline Curves, 600 B.C. to 600 A.D.|journal=[[Social Science History]]|volume=3|issue=3/4|page=117|doi=10.2307/1170959|jstor=1170959}}</ref> The list is not exhaustive owing to a lack of available data for several empires; for this reason and because of the inherent uncertainty in the estimates, no rankings are given.