I wrote about this several years ago on one of Wizards of the Coast’s (WotC) Dungeons and Dragons (D&D) forums. The issue I have is that Eberron is a large continent, on par with the continental USA, and yet the population is incredibly low. To give an example, I like to focus on Breland. Breland is somewhat similar to the USA, in that they have a large industrial base, and are not structured in an extreme fashion (Anduair and Cyre have their magocracies, Thrane has its theocracy, and Karrnath is filled with undead). They’re not described as being a cold northern nation like Karrnath, or a breadbasket like Aundair, but “Temperate in the north, tropical in the south”. They balance magic and martial skill, and really have a feel of a melting pot society.
In the “Five Nations” book, Breland is listed as having a population of 3.7 million and an area of 1.8 million square miles. That’s about 2 people per square mile, which is half the population density of either Mongolia or Western Sahara. Even Chad, the nation at the bottom of the Legatum Prosperity Index, has a population density of 20 people per square mile. Given some medieval examples of 100 people per square mile in France, 90 in Germany, and 40 in the Britain, this feels horribly skewed. While it could be explained that this incredibly low population density comes as a result of the devastation of the Last War (a century long internecine fight over which of the five nations would rise to control the previous combined empire, Galifar), it doesn’t add up. Even if Breland had a prewar population density of Britain (72 million), they would have to lose about 3% of their population each year for a hundred years. By comparison, the US Civil War only lost about 0.8% of their population each year (averaged per year), and I doubt it could be considered to have been a small war. A war as devastating so as to lose 3% of your population each year would push any nation to revolution. Even looking at the raw numbers, losing 68.3 million people in war would put Breland alone in the ranks of the total losses in World War II.
Ultimately the losses in the Last War could end up on one of two ends; either it was significant, but sustainable, like the USA and it’s war in Iraq and Afghanistan, or devastating but irretrievable, like the Hundred Years War, where the populations so feared for their sovereignty that they were willing to keep going. The former seems to be the direction the authors of the Eberron series decided to take, based on the continued existence of the non-territorial Dragonmarked Houses (equivalent of stateless corporations); in a full out, all in war, these Houses would find their assets seized. The idea that House Cannith could produce Warforged for all sides of the conflict, despite apparently only having a few creation forges; had the creation forges been more widespread, than the knowledge of how they are constructed would be similarly widespread, and not a closely guarded secret of House Cannith.
Unlike the authors of Eberron, I prefer to see the Last War on the devastating but irretrievable side of things. While they also suffered through the Black Death at the same time, France and England lost between a third and a half of their population from the beginning of the Hundred Years War to its end, 116 years later. I imagine things to have been worse in Eberron. With a starting population density of 80 people per square mile (144 million total), but with an attrition rate of 0.5% per year (sustainable, but heavy), after 102 years of war, Breland would have a population of 86 million, or roughly 50 people per square mile.
Now here is where the fun with the Doomesday Book comes in. S. John Ross wrote a wonderful article “Medieval Demographics Made Easy”, in which he lists some of the statistics I used above, alongside observations of number of cities, professions, etc. to be able to give a robust view of a medieval nation. Using a calculator made by Erin D. Smale, one can have a look at the before and after pictures of Breland.
Going into the Last War, Breland would have 144 million people, the vast majority of which would be living in villages. It could support 5 Universities, and would have around 2100 actively used fortifications in civilized areas and about 700 in the wilderness. In addition there would be about 5600 abandoned fortifications (4200 of which would be in the wilderness; this vast number of ruins is due to the settlement by the empire building Goblinoids 38000 years ago … only 1 in 3 were built by Humans). There would be 4 major cities, 300 cities (around 12000 people per city), 1700 towns (5000 per town), and 285000 villages (450 per village).
Coming out of the Last War, Breland would have 86 million, with 2 Universities with another barely hanging on. 1800 actively used fortifications would remain (450 in the wilderness). There would be 3 major cities, 185 cities, 1100 towns, and 180000 villages.
The toll of the war would be the loss of 300 fortifications, 1 major city, 115 cities, 600 towns, and about 100000 villages. This doesn’t mean that these towns and villages would be completely empty, but to maintain the same population levels (12000, 5000, and 450), this is what the calculator spits out. While the nation would have lost 40% of its total population, I would suspect that each centre of civilization would only drop by about 20%, as people would move to areas of higher population density for safety in numbers. So a typical city would only have about 10000, a town 4000, and a village 400. This would result in 225 cities, 1275 towns, and 215000 villages surviving (or 75 cities, 425, and 70000 villages lost).
Each city, town, and village could be expected to have plenty of empty buildings in which nefarious (and adventure generating) activities could occur, and the abandoned settlements would make for great bases of operations (and in their own way, dungeons). Want to have a chase through a city, but don’t want to have to deal with the potential side effects of area of effect spells being hurled back and forth? Have it set in scarcely populated city. Want to give your players something to grow into? Turn over authority for running a former city that has the population of a town now to them; they can decide whether or not to spruce up that crumbling cathedral, or maybe repurpose it into their new headquarters. While the viability of half of the universities might be over, their might still have buildings standing, and there are all sorts of opportunities for secret labs, libraries for plundering, and containment wards wearing out. New Cyre might be built in an area that was evacuated during the war (it is right between Thrane and Cyre, an ideal place for battles to take place), prompting survivors to ask adventurers to retrieve something they left behind. That veteran who knows the location of a cache of weapons needed in a new conflict? He’s gone back to his home village and is the only one living there, littering it with traps to foil off potential looters.
All in all, it gives the excuse to have lots of ruins, both new and very old (those Goblinoid ruins would be ancient), of a variety of styles and sizes, to be able to run adventures in.