Fantasy Demographics, or: Why Elves and Orcs Fight Different Wars

Note: This post deals with Real World ideas, concepts, or choices that are very personal. It is not meant to offend but is just a discussion of how these factors impact fantasy role playing game campaigns. Thanks.
  Waaaaay back when, my Dad took me to see Soylent Green. Now, I was very young, but in my father's defense we both love science fiction movies, so we went anyway. This began my rather odd hobby of studying demographics (which led me to reject the threat of overpopulation by 5th grade, but that is another story). Thus there was something in both the Complete Book of Elves and the Complete Book of Dwarves which just intrigued me. In the complete CBoE they state that the average Elven female has 2 children. In the CBoD they state that the average Dwarf female has 3 kids, but 2/3 of all births are males.
  Why does this matter?
  Math.
  Not to get too wonky (although I can talk about demographics for literally hours. And I am not using 'literally' for emphasis, I mean it literally) (see what I did there?), but a key metric in demographics is Total Fertility Rate (TFR for short) which is, simply, 'how many children does each woman in a population have, on average?'. TFR means a lot - it allows you to calculate the growth or shrinkage of future generation, determine the demographic momentum of a society, all sorts of really... boring... to... anyone... else... stuff....
  Yeah.
  Anyway, when the books say 'the average Elf female has two kids' this means 'the TFR is 2'. This is important because in the Real World replacement TFR (the TFR where the population neither grows nor shrinks over generations) is between 2.1 and 2.4 - each woman has just over 2 kids each on average. Since a certain number of people never have kids for a variety of reasons, it must be above a flat 2.0. In a modern industrialized nation like, oh, France, 2.1 is equilibrium. In a modern nation with a higher rate of mortality for youth it is more like 2.4.
  Here's the point, though - in pre-modern societies replacement TFR was more like 3.5-4.5. Why? Poorer health care and a higher mortality rate. Remember, the reason the average lifespan before the mid-20th Century was 35-40 for most of the world was because so many children died - if you lived to be 14-16 you were almost certainly going to live to be 75-80! Well, barring other factors. Like war.
  Chronic war really increases the replacement TFR number, for obvious reasons. Plague can do the same.
  Well, the CBoE said 2, but maybe they reaslly meant, oh, 2.3. With magical healing, a natural resistance to disease, etc., this probably means that Elves have a stable population, barring war.
  Let's talk about Dwarves for a moment.
  In the Real World we assume a gender ratio of about 50/50, so the 66/34 male/female of the Dwarves is really important.This means if you start with 300 Dwarves you will only have 100 couples (it takes two to make little dwarves and, more importantly, TFR is tied to the number of females). If they have a TFR of 3 that means the next generation will be = 300 Dwarves. Also perfect equilibrium since that generation will also have 100 females
  "OK," I hear you say, "so the generations are stable, so what?"
  One, it means that if you accept these numbers Dwarves and Elves can't really expand - if there is already a city that houses 2,000 Dwarves why build a new one? After all, there is no population growth. Sending people off is a drain of the most important resource of a society - the people. There are probably a number of social pressures to avoid this.
  Two, it will have a huge impact on how Dwarves and especially Elves go to war. Here are some of my thoughts on this:
  While Dwarves have an 'excess' male population (the 33% of each generation that will have no wife) allowing them to go to war relatively easily, women and children are virtually irreplaceable. So while male Dwarves roaming the mountains prospecting and killing Orcs for fun might be common, they will almost certainly guard their women and children fiercely. This is a simple explanation for why you traditionally never see Dwarven women - they are quite directly the most precious thing in Dwarf society.
  For Elves it is even more extreme - any loss of life might not be replaced for two or more generations. That is pretty serious.
  This means the Elves must really strive to limit battle deaths and while Dwarves can sustain some heavy losses of life on the battlefield women are too precious to risk.
  Which leads me to a fantasy element - lifespan of non-humans.
  It takes a human about 16 years to be considered an adult and human generations are counted as about 25 years. If we follow the age guidelines in the DMG (and why wouldn't we?) it takes a Dwarf about 60 years to mature and an elf about 120. With a bit of extrapolation we can guess that a Dwarven generation is about, oh, 60 years and an Elven generation is about 250.
  Wow. That's big.
  Why? because it takes at least a generation to recover from a major loss of life. World War I caused the death of a huge number of young men. One of the reasons World War Ii was a generation later is, arguably, the hostiles needed to wait until the next generation finished growing up to continue the fighting. The Black Death caused so much loss of life that it really took five generations for Europe to recover.
  This means that it would take the Dwarves 75 years to recover from a war that killed their 'excess' males and about 30% of the rest of the males. This means an Elven society struck with something like the Black Death wouldn't recover for more than a millenium. That is high stakes stuff.
  Let's change tacks just a little bit and think about Orcs. We can extrapolate that they mature around 12 and that an Orcish generation is, oh, 20 years. We know they are 'fecund' because we are told they are. What does this mean in comparison with Elves? Well, in the Real World there are societies that reached TFRs of 9+ in the 20th Century, so 'fecund' could be quite a large number! But let's just assume that between disease, violence, and generally being Lawful Evil Orcish societies grow about 25% per generation.
  What does this mean? More directly, what does this mean for a campaign (since this is about a game, after all)?
  Here is a scenario;
  The Orcish tribes and the Elven kingdom have been on edge for a decade, but now war is really begun. The Elves are smarter, better trained, have better gear, and have more spell casters. The Orcs are more disciplined and there are many more combatants. When they begin the war there are 3,000 Elven soldiers (out of a kingdom of 20,000) and 7,500 Orcish warriors (out of 20,000 Orcs).
  After 5 years of brutal fighting the Elves prevail; they slaughter over 5,000 Orcs while losing only 1,000 Elves. The Elves return to their homes, triumphant, and the good feelings and other factors cause a spike in births, meaning the next generation of Elves will be about 10% larger.
  Humiliated, the Orcs retreat to their homes. There is no surge for them. At this point, the Year of the Great Battle the two sides are roughly as follows;
  Orcs: 3,500 surviving warriors. 7,500 potential warriors not yet mature from the 2nd generation. And 6,000 females with mates available to birth the 3rd generation.
  Elves: 2,000 surviving soldiers. 3,000 potential soldiers not yet mature from the second generation. And 9,000 females with mates to birth the 3rd generation.
 In Year after the Great Battle (YGB) 20 the second generation of Orcish warriors are mature and ready to fight - all 7,500 of them! They face off against - the first generation Elvish warriors again. After all, the young Elves still have over two centuries to mature! The Orcs are young and the cream of their army dies in the Great Battle. The Elves are battle-hardened and fierce, so this time the Elves kill another 4,000 Orcs but only lose 500 Elves. So in the second generation we have;
  Orcs: 3,500 surviving warriors. 7,500 potential warriors from the 3rd generation (25% growth, remember?). 6,000 females with mates to birth the 4th generation.
  Elves: 1,500 surviving soldiers. 3,000 potential soldiers from the 2nd generation. 9,000 females that will eventually birth 2,700 soldiers in the 3rd generation.
  Reeling from two defeats in two generations, the Orcs wait, biding their time and skirmishing with Humand and Dwarven forces in raids, raids which whittle down their comabt numbers but mean their warriors are experienced.. Finally in YGB 60 the 4th generation of Orc warriors, whittled down to 7,500 (remember that 25% growth?) but battle-hardened face off against - the 1,500 surviving 1st generation Elven warriors! As evenly matched individually as the first battle, but incredibly outnumbered, the Elves fight as defensively as possible. They barely manage to drive off the Orcs losing another 1,000 elves to 4,000 Orcs.
  Barely able to send 500 soldiers to the field, the Elves retreat into the mountains.
  As you can see, the humanoid races, with their higher fertility and shorter generations, have a massive advantage in warfare over multiple generations!
  In other words, if Elves and Dwarves do have such low fertility, they are going to be wiped out. As a matter of fact, as DM you need to explain why they haven't been wiped out already.
  Please allow me to digress from fantasy to reality for just a moment. I am going to assume that most readers of this blog like most roleplayers are from nations with low birthrates. This is, historically, an anomaly. While real world demographics do show periods of stability and periods of decline, these were caused by bad weather and plague - birthrates remained high relative to modern birthrates. While the majority of the current world is below replacement TFR this is very unusual.
  Back to FRPGs. As you can see from the example I give above, have only replacement TFR is a big problem because it means that societies can't replace major losses in anything approaching a reasonable amount of time! For this reason in my campaigns I tend to have birthrates higher. Add in the fact that FRPG worlds tend to be shockingly lethal, I tend to make them much higher than you see in the modern world, much more akin to Europe of the High Middle Ages. I essentially assume that per generation population growth for Humans is about 30%, for Halflings it is 25%, for Elves, Gnomes, and Dwarves it is 15% and for the major humanoid races it is 40%-60% (not counting war or disease for any of these). I also have the sex ratio be about 50/50 for everyone but Dwarves where it is 55/45 male/female.
  Even with more reasonable TFRs, though, the issue of the length of generations remains - Orcs can go through almost 4 generations before Dwarves get to 2. For Elves it is closer to 12 generations to 2. This will have a profound effect upon how the various races wage war.
  First, the various bonuses Dwarves and Elves have (bonuses vs. certain races or with certain weapons) make sense because of their longer lives. The same applies to the greater numbers of powerful individuals in their forces. In any given battle Dwarves or Elves will prevail over Orcs of the same number. It will be more lopsided in their favor against Goblins and much more even against Hobgoblins. But Dwarves and Elves must do their utmost to avoid a long-term war of attrition because they simply can't win such a war.
  Suddenly, there is a reason Dwarves built such strong mountain fortresses and Elves live in thick forests with many sylvan allies; these positions are defensive, giving them the advantage, and can give them better warning of potential attacks. Both races will be as selective as possible about engaging forces they cannot overwhelm and must limit their losses as best they can.
  In a similar vein, Gnomes and Halflings make a lot more 'sense', too. The Halflings have great stealth and skills with missile weapons because they rely upon avoidance and ambush. Gnomes, with their illusions, are natural commandos. Like Dwarves and Elves they have these skills because they need them to survive as a society.
  Humanoids, on the other hand, are much more like hammers than rapiers. Their goal in war is to close with and engage the enemy with as much force as possible. With their numbers than can afford to be profligate on the battlefield because they recover from the loss of soldiers faster than their foes. Wave attacks by Goblins to 'soften up' the front lines for the hammer blow of a Hobgoblin charge may seem like a terrific loss of life but every Dwarf they kill is one less Dwarf their grandchildren will have to fight!
  This can also explain why Humans so often seem dominant in FRPGs; with a birthrate and generation length much closer to the Humanoids they are both much more capable for fighting humanoids on their own terms and invaluable allies to the other demi-human races.
  Please think about it and I hope this can add to your campaigns.