I'm attempting to make a large tropical island, roughly 120k square miles in area, with a centralized monarch-based authority. Is this feasible, or will it quickly devolve into smaller kingdoms, separate in all but name?

If not, what's the upper limit?

If any details are needed, the island has fertile land, is relatively equatorial, and is in stereotypical no-gunpowder feudal medieval Europe.

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    $\begingroup$ The medieval cap covers about 1000 years of history, it's a tad large... $\endgroup$
    – L.Dutch
    Nov 29, 2021 at 17:40
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    $\begingroup$ More Details Please - Are we assuming feudalism? - Are the surrounding islands a threat such that your kingdom needs to maintain a geographically-distributed standing army or does the island's isolation from external threats allow for military might to be concentrated at the Capitol. - Do they have horses or camels or some other form of "fast" transportation? $\endgroup$ Nov 29, 2021 at 17:58
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    $\begingroup$ That's almost impossible to answer since it depends on what the unifying factors (e.g. common culture/language/religion, quality of leadership, external threats, etc.) versus disintegrative factors are. It's certainly not impossible; the Byzantine empire lasted for centuries and was larger. $\endgroup$ Nov 29, 2021 at 17:59
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    $\begingroup$ Note that Japan is ~146K square miles in area, and for much of its history was united under a single rule, either that of the Mikado (often ceremonial), or the Shogun. $\endgroup$
    – jamesqf
    Nov 29, 2021 at 18:02
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    $\begingroup$ @Alexander: The Carolingian Empire did fracture, but the largest and most durable piece was France and it was larger than the requested 120,000 square miles. And it did last for quite a while. In fact, as far as I know, it still exists. $\endgroup$
    – AlexP
    Nov 29, 2021 at 19:29

6 Answers 6


I went to the Wikipedia list of largest empires, and to the specific list of largest empires by land area. I sorted it by date by clicking on one of the little triangles in the date column.

The middle ages lasted from about 476 to 1453, or from about 500 to 1500, or whatever dates you chose to use.

Assuming that you don't want examples of African (The Mali Empire), Asian (The Mongol Empire), or American empires (the Inca Empire), I looked for empires which were at least partially European.

Empire Square Miles Year
Byzantine Empire (Eastern Roman) 1,040k - 1,080k 555 or 450
Kievan Rus' 810k 1000
Francia (the Frankish realm or Carolingian Empire) 460k 814
Polish–Lithuanian Commonwealth 420k 1480 or 1650
Holy Roman Empire * 390k 1050
Caliphate of Córdoba (in Spain) 230k 1000
Kingdom of France (Middle Ages) 150k 1250
Latin Empire 140k 1204

* Omits the areas of several vassal states

The area of the eastern section of the Roman Empire, the so called "Byzantine" empire, fluctuated a lot during the Middle Ages.

A Wikipedia table gives examples:


The smallest area of the "Byzantine" Empire listed there is 420,000 square kilometers or 162,162 square miles in 1320, though it got smaller in later decades, eventually passing below your goal of 120,000 square miles.

So you see that a number of more or less medieval and more or less European states had larger areas than 120,000 square miles or 310,798.573 square kilometers.

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    $\begingroup$ Wouldn't population be more relevant than, or equally relevant to, geographic scale? Also, the HRE wasn't really meaningfully controlled by one monarch, it has authority closer to that of the UN than a conventional sovereign state. $\endgroup$
    – ohwilleke
    Nov 29, 2021 at 20:42
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    $\begingroup$ @ohwilleke: It was a bit more similar to the EU than the UN. It did have a sort-of common civil justice system (more Byzantine than Byzantium itself, but there it was one), it did have a sort-of imperial Parliament, and it did have a common administrative structure (albeit rather theoretical). But yes, it was never a "country" in any meaningul acception of the word; for the most striking example, each component state always imposed customs duties at their borders, had its own criminal justice system, its own currency etc. $\endgroup$
    – AlexP
    Nov 29, 2021 at 20:51
  • $\begingroup$ @AlexP "It was a bit more similar to the EU than the UN." Fair. $\endgroup$
    – ohwilleke
    Nov 29, 2021 at 22:52
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    $\begingroup$ The Byzantine Empire, certainly in 555 but even in 1000, is better thought of as a lingering piece of antiquity. Medieval societies, with less centralization, less professionalization and less state capacity, were unable to match it. Carolingian Empire is unambiguously medieval, though. $\endgroup$
    – dspeyer
    Nov 30, 2021 at 1:01

Compared to some Empires, 120k is tiny

To put into comparison how feasible this is, we just need to take a look at the Roman Empire.

In 25 BCE, the estimated area of Rome was about 1,060,000 square miles or about 2,750,000 km^2.

This was long before medieval times, so if it was possible then, why wouldn't it be possible in a setting that is even further in the future?

Other massive empires included the Mongol Empire, which was even larger in comparison. In 1309 it is estimated to have had about 24,000,000 km^2 area (which is about 9,300,000 square miles).

If the Mongols and the Romans were able to pull off empires that were significantly larger than this, then it is certainly feasible.

The Mongols are often considered the largest land-based empire in history, second only to the British Empire, and the British Empire had the advantage of technology that was definitely not available to the Mongols. If you are looking for the largest an empire can be with only medieval technology, the Mongol Empire is, historically speaking, as large as it can get.

You also have the advantage that this is an island locked in by the ocean. Once you've conquered all the lands within the island, the people either have to accept the rule or hope they can somehow take a boat to another land.

As for the question of, "would it dissolve into smaller kingdoms?" that depends on a lot of factors.

Generally speaking, empires break into smaller bits because they have overextended themselves. If they don't have the manpower or infrastructure to maintain such a massive landmass, then it will eventually break into pieces, but an island of this size could remain relatively stable. While massive empires crumble easily, a reasonably-sized nation with decent leadership can last a very long time.

Another factor is culture. The people of the island might not want to be under the thumb of an emperor in the first place. For example, there might be hundreds of languages and religions on the island, but the empire only wants one language and one religion. This could lead to the island dividing into several smaller nations and cultures.

  • $\begingroup$ On the other hand, the Mongol Empire was a very short-lived structure... $\endgroup$
    – AlexP
    Nov 29, 2021 at 19:17

It's possible

Although there are size limits in various ways to countries in certain time periods, 120km² certainly isn't the biggest. Spain and France did have turmoil, but didn't completely fall apart. With some adaptations I think they can stay ok.

There's some recipes that can help. A common enemy. Like an area outside the island that can be fought over. It can be the population in revolt or other countries that attack it, but either can push the inhabitants together. Other things are a common relatively background. Some social views that allow them to stick together. Dependency on each other. All can contribute. If these stay relatively constant and change isn't fast, then the country can be stable for a long time.

The most dangerous of all is change. Change means instability, which can change ideas and splinter a country. Change isn't bad necessarily, but just has that potential.

A maximum is difficult to estimate. We have examples where the size tore up countries, like the Roman empire. Through it shows a limit, it doesn't show the limit. With some differences it might've lasted longer.

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    $\begingroup$ During most of the Middle Ages, most of the Iberian Peninsula was an Arabic-speaking Muslim territory. At some times it was indeed unified under a central authority, but in those times it was Al Andalus and definitely not Spain. $\endgroup$
    – AlexP
    Nov 29, 2021 at 19:57

The size seems alright

The carolingian empire covered over 400k square miles before it collapsed into three soon to be two kingdoms. The Holy Roman Empire was more stable and had about 400k sq mi as well.

Size will not be the main issue, but the tropical climate might be

Tropical climate is more prone to diseases and tend to have lower population density, which in turn make it harder for a central authority keep the region together.

I would recommend putting the isle closer to the tropics than the equator, there's where civilization tend to form, like Mayan, Indians or Khmer. The regions closer to the equator tend to remain tribal and unpopulated, like the Congo, Amazonas or Borneo. That is, unless there is something that makes it more inhabitable, I can think of Indonesia for being in a major trade route and the Marajoara in the Amazonas delta (relying on fishing and a flooding savana).

For reference I would recommend Khmer Empire, you can mixture it with more western european element, but those radically different climates tend to produce radically different societies.

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    $\begingroup$ "The regions closer to the equator tend to remain tribal and unpopulated": like India, for example. A famously underpopulated country in medieval times. (India reaches about 8° northern latitude.) (And the question says tropical not equatorial. India certainly qualifies as tropical, and it was always teeming with civilized people.) $\endgroup$
    – AlexP
    Nov 29, 2021 at 20:02
  • $\begingroup$ @AlexP The OP says "...is relatively equatorial..." $\endgroup$
    – Nosajimiki
    Nov 29, 2021 at 20:28
  • $\begingroup$ @AlexP its about climate, not geographic position (I suppose I could have explain that instead of going with where I expect to find each climate). India and Sri Lanka are mostly tropical savannah and tropical monsoon climates, the real problem is in the tropical humid where the rain just won't stop the whole damn year. $\endgroup$
    – LuizPSR
    Nov 30, 2021 at 3:57
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    $\begingroup$ "The rain won't stop": Actually it is very predictable, it rains daily in the afternoon. No, this does not condemn the region to "remain tribal and unpopulated". For a well-known example, the island of Java has a typical equatorial climate, and this did not stop it from having a very civilized thank you history during the time frame corresponding to the European Middle Ages; you may have heard of Borobudur, for example. (And you find underpopulated tribal areas in all climates, cold, temperate or cold.) $\endgroup$
    – AlexP
    Nov 30, 2021 at 9:29

I haven read all of the answers, but most site historical sources for who occupied what how much land. The Mongol empire comes up a lot. Which, is true, likely was the empire with the largest land area. However, Most of the time it had existed they were either expanding or collapsing. There was never really any sustained Mongol Empire for any meaningful length of time. The answer to your question is, there is no upper limit. It entirely depends on engrained culture and the sophistication of the cultures adopted laws. If the culture fragments in a way that is destructive to the body of the governments imposed system of laws, and those laws are not sophisticated enough to adapt. The society will collapse.
Rome wasn't conquered by barbarians, it was fell when the state began to disintegrate (for many reasons) and its laws and culture couldn't hold it self together thus and was unable to react to the uprisings it had easily dealt with for centuries. Size and population does play a major role, however those are only forces that any government has to deal with whether it is a town or a content. How it deals with those forces is the point at hand.
If you have a Government that is steady, forethinking and consistent, a strong and well regulated obedient army, along with a homogenous spiritual population, the only thing that county should fear would be decadence(That part is opinion). Steady, forethinking and consistent doesn't necessarily mean good or bad. They could be brutally authoritarian or strict egalitarian as long as the culture allows such.


Assuming a roughly circular shape, that's only about 400km across. Not too bad for horse riders to cover if you put the capital city roughly in the center, especially with relay stations at regular intervals.

Even signal towers with smoke and/or fire signals can work, maybe have both.

As already pointed out, similar sized fiefdoms of various natures existed in reality within the rough technological and social era you're considering, this shows how they could exist.

Of course it depends on geography and culture as well. If the area is hard to navigate, control over outlying regions becomes next to impossible (which is why there are for example so many separate tribes in New Guinea, before helicopters and aircraft it was pretty much impossible to travel from one valley to the next there because of the terrain, so different 'nations' could exist within a few kilometers of each other and never even know about each other).

But you will have to create a cohesive culture across your land, with relatively small regional variations. Either that or have large garrisons to suppress unrest and rebellion in the outlying provinces, which brings its own problems as the leaders of those garrisons might just decide to lead said rebellion rather than suppress it (happened during the late Roman era too, and maybe a plot element for you to use).


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