To Rule the Earth...

No one person has ever achieved rulership over the whole planet. Which states have come closest to this measure? What follows is a table of the 25 largest states and empires to have held sway over the earth at one time or another. The figures for their sizes are approximations for the most part - many of these states held only vague or ill-defined frontiers. The figures given are also drawn from the period of maximum extent for the nation involved; thus, the Portuguese figures exclude Oman and Malacca (among numerous other Portuguese bases), since their occupation and withdrawal predated the later Portuguese holdings. Similar circumstances obtain for other empires, and are noted in the comments. As a comparison to the land surface that is available, note that the habitable portion of the globe (i.e. excluding Antarctica) extends over roughly 52, 677,000 square miles (136,433,400 sq. km.): so, the largest of these entities reached about one quarter of the whole.

The British Empire and Commonwealth
The greatest extent of the British Empire was achieved between 1918 and 1922. The figures exclude the eastern seaboard of the United States, which became independent long before the British colonial expansion of the 19th century.

14,157,000 sq. miles (36,666,630 sq. km.)

The Soviet Empire
The Communist states were never entirely under a single ruler - Although Josef Stalin probably came closest 1948-53. The main division was between the Soviet Bloc, led by Russia, and the Eastern Bloc, led by China. The area given for the whole Communist world does not include later, semi-nonaligned states such as Angola, Tanzania, or Laos.

The entire Communist world	13,800,000 sq. miles (35,742,000 sq. km.)
The Soviet Bloc (incl. Cuba)	09,883,591 sq. miles (25,598,500 sq. km.)

The Mongol Empire
The greatest extent of the Mongol hegemony was reached in
roughly 1238-68.

12,800,000 sq. miles (33,152,000 sq. km.)

The Spanish Colonial Empire
At its largest reach, roughly 1740-1790 Spain controlled about half of South America, more than a third of North America, and had significant holdings in the Pacific basin.

07,500,000 sq. miles (19,425,000 sq. km.)

The Russian Federation
Russia is, of course, a subunit and the core of the Soviet Empire noted above. Even in its reduced state, it is still by far the largest single state on the planet.

06,592,000 sq. miles (17,073,280 sq. km.)

The Fascist Axis
The Axis powers of the World War II era were never under a single ruler, they were a group of three major powers and a handful of minor ones. Some of the lesser states were, in fact, only nominally associated with the Axis, owing to the needs of defence against mutual foes (as in the case of Finland, which I do not include), or outright intimidation, as in the case of Thailand (which I do).

Japanese territory and conquests	02,864,000 sq. miles (07,417,760 sq. km.)
German territory and conquests	01,420,000 sq. miles (03,677,800 sq. km.)
Italian territory and conquests	00840,000 sq. miles (02175600 sq. km.)
Other Axis allies	00249,800 sq. miles (00646982 sq. km.)
total	05,373,800 sq. miles (13,918,142 sq. km.)

The Caliphate
The Early Caliphate was a remarkable thing - a vast stretch of territory spanning Spain, North Africa, the Middle East, Iran, and much of Central Asia: all of which absorbed by Arab conquerors in a bit less than 100 years. Too vast to be stable, it began to fragment less than 200 years after.

05,100,000 sq. miles (13,209,000 sq. km.)

The French Colonial Empire
The French colonial experience was primarily within Africa, although there were significant territories in Asia and the Americas as well. The figures do not include Quebec or Louisiana, long lost before French colonial expansion in the 19th century.

04,863,000 sq. miles (12,595,170 sq. km.)

The Chinese Empire
Modern China is somewhat smaller than the figures show - they indicate the approximate size of the state governed by the Qing Emperors during the late 18th and early 19th centuries, which included Tibet and Mongolia as dependencies.

04,300,000 sq. miles (11,137,000 sq. km.)

The Portuguese Colonial Empire
At it's greatest extent, c. 1815-1820, Portugal controlled major territories in South America and Africa. Like many other colonial powers, Portugal had held a previous empire (centered mostly in Asia) which was lost.

04,000,000 sq. miles (10,360,000 sq. km.)

Dominion of Canada
Canada is a subunit of the British Commonwealth and, as an independent state, the second largest on earth at this time.

03,849,000 sq. miles (09,968,910 sq. km.)

United States of America
The figures reflect the United States at its greatest territorial influence, circa 1915-1934, when it controlled not only the Philippines, but also had occupied Haiti.

03,746,087 sq. miles (09,702,365 sq. km.)

Federative Republic of Brazil
Brazil is the major subunit of the Portuguese colonial empire, and remains today the fifth largest state in the world in terms of territory.

03,300,000 sq. miles (08,547,000 sq. km.)

Commonwealth of Australia
This continent-sized land mass hosts but a single state, one which is significantly larger than all the great empires of classical times. The figures are for the period 1918-1975, when Australia administered Papua and New Guinea.

03,147,700 sq. miles (08,152,550 sq. km.)

The Persian Empire
This is the oldest of the super-states listed herein - it is the vast empire successfully held off by the Greek city-states in the 5th century BCE.

02,382,000 sq. miles (06,169,380 sq. km.)

The Seljuq Empire
The Seljuqs were a Turkish people who established a Middle Eastern Empire in the late 11th century CE. It swiftly fragmented into more localized spheres of influence, notably in Iran, Anatolia, and the Fertile Crescent region.

02,300,000 sq. miles (05,957,000 sq. km.)

The Roman Empire
The Romans were at their greatest extent in the early 2nd century of the Common Era, when Trajan briefly annexed Mesopotamia.

02,200,000 sq. miles (05,698,000 sq. km.)

The Ottoman Empire
The Osmanli Turks established a state in Bithynia which eventually grew to encompass Anatolia, the Levant, the Balkans, North Africa, Crimea, the Caucasus, and western Arabia as far south as Yemen.

02,160,000 sq. miles (05,594,400 sq. km.)

The Macedonian Empire
Alexander the Great briefly established a vast empire on the carcase of the Persian super-state (#15); but it fragmented almost immediately after his death.

02,100,000 sq. miles (05,439,000 sq. km.)

Mexico
When Mexico became independent (first as an Empire and shortly thereafter a republic) in 1821, it inherited a vast stretch of former Spanish claims reaching from Nevada to Costa Rica. The figures are for the period 1821-23, after which Central America broke away.

01,890,983 sq. miles (04,871,733 sq. km.)

Almoravid Empire
The Almoravids were a western Berber folk who boiled out of Mauretania in the 11th century, to rapidly encompass all of northwestern Africa and about half of Spain-Portugal for a brief time. Establishing a radically puritanical sect of Islam, and founding the city of Marrakesh in 1065, they were at the height of their influence c. 1105-1145.

01,500,000 sq. miles (03,885,000 sq. km.)

Timur's Empire
Timur the Lame was a tribal leader of Mongol extraction who set up a Middle Eastern empire centered around Iran in the period between 1380 and 1405.

1,445,000 sq. miles (03,742,550 sq. km.)

The Mughal Empire
There have been large, centralized states on the Indian
subcontinent for a very long while - the Mughal empire in the latter half of the 17th century probably achieved the greatest size, although the current republic isn't much smaller.

01,425,000 sq. miles ( 2,294,250 sq. km.)

The Seleucid Empire
The Seleucid state was a successor empire to Alexander's
Macedonian Empire (#19). At it's greatest extent, it reached from western Anatolia to Afghanistan.

01,325,000 sq. miles (03,431,750 sq. km.)

Argentine Republic
Aside from the Andean highlands, Argentina encompasses all the southernmost reach of South America.

01,073,400 sq. miles (02,780,106 sq. km.)

Republic of Kazakhstan
Kazakhstan is a vast semi-arid region of central Asia, and a subunit within the Soviet Empire up until its independence in 1991.

01,052,090 sq. miles (02,724,913 sq. km.)

The Ghaznavid Empire
A Mediaeval state within what is now Afghanistan, Pakistan, portions of central Asia, and eastern Iran. It's greatest extent was in the early 11th century.

01,000,000 sq. miles (02,590,000 sq. km.)

Note: I am asked at fairly regular intervals about a possibly missing element in this list, namely, Tiwantinsuya, the Incan Empire of the later 15th and early 16th centuries. Correspondents will mention figures ranging anywhere from 2.5 million square miles (6.475 sq. km.) to 7.5 million square miles (19.425 sq. km.). Some writers have cited a book by Charles Mann called "1491", a description of the Western Hemisphere just before the arrival of Europeans in support of their contention - apparently Mann alleges that the Inca controlled a region comparable in size to that of the Ottoman or Roman Empires.

I must disagree with Mr. Mann. Let's do the math - assume half of Peru (actually, historical maps that I've consulted usually give less than that, about 1/3 to 40 percent, but we'll assume half), that yields about 250,000 sq. miles. Assume all of Ecuador, another 100,000. Assume about 1/3 of Bolivia; that will give about 130,000. Add maybe half of Chile (most maps I've seen aren't as generous), another 150,000. And add perhaps the northern tip of Argentina, maybe 1/10 for another 100,000. Under these very generous assumptions, the total comes to about 730,000. If you want to throw in some smidgens of Colombia, you could maybe push 750,000, very close to the size of modern Mexico. You would have to toss in all the rest of Peru just to reach 1 million, something historical works never do because the Inca aren't known to have penetrated to any significant extent into the Amazon Basin. As for the highest figures I've seen (7.5 million sq. miles), well, all of South America only comes to 6.89 million - the 7.5 million figure is about identical to the entirety of the Spanish colonial Empire at it's greatest extent (#4 above), from Patagonia to Utah; I'm certain the later Maya, the Aztecs, and the early Apache would be astonished to learn that they were subjects of Cuzco.

The simple fact of the matter is that the domain of the Inca wasn't enormous (the Aztec territory was even smaller) physically, albeit it's influence and power were great. But size isn't everything - consider the clout and influence of the Vatican as compared to it's physical area.

Bruce R. Gordon's Regnal Chronologies