Let's talk some statistics.
If we can review my experience system for a moment, we find that for every point of damage an individual takes, he or she gains 20 experience. For every point of damage the individual causes, 10 experience. And all the damage that is taken by any one side in a fight is multiplied by another 20 experience, and divided equally among all the participants in the battle on that side - even if those participants never caused, or took a point of damage. If they tried to fight, or they supported those who fought with spells or by keeping them alive in some manner, they are entitled to experience from the event. It is important to note, in addition, that individuals do not have to die or even win the battle in order to gain experience. They can lose, or fail to kill the foe, and still walk away more experienced than when they began.
Those are my rules. Other people play by other rules, but this is my blog and my world, so here we play by mine.
What this means is that for every point of damage caused, a total of 50 experience is rewarded: 10 to the attackers, 40 to the defenders. This would be lopsided, but it should be noted that experience has no influence upon combat while the combat is ongoing. Experience is only rewarded AFTER the combat is over.
Thus, if someone takes enough damage to kill them, dying in the combat, that someone never actually gets that experience; the 20 x.p. that they would get for losing their own 8 or 80 hit points is gone. However, the bonus 20 x.p., that which is divided among the survivors, is still gained by those who watch or otherwise experience that individual's death.
So after a battle, if people die, some experience is lost; but those who live still get at least 20 experience per hit point suffered - and likely more besides, as they are unlikely to be unscathed or unsuccessful in causing damage of their own.
In a war, let us make a gross estimate of 40% of the losing side being killed, and perhaps 20% of the winning side. I have no averages to back this up - but given the number of battles I've researched, and the number of battles I've run in D&D, this seems reasonable. Most wars do not end with one side being slaughtered - that side routs or surrenders first. It's rare that everyone on a side is killed, and in any case, its more common that two sides in a battle will both pull back before more than 10% of either side dies. Most battles are the result of two forces feeling each other out before the last ditch all-or-nothing battle is fought.
I state openly the numbers are unreliable. I have no reliable numbers, and I want to write this post, so here we are. No doubt, the quibbling quandrists will insist on having their picky moment over the exactitude of numbers that just don't exist, but I'm not interested. I'd like to calculate the effects of the proposal. Feel free to pick your own numbers and make your own calculations.
Okay, so 30% of the participants are killed. Some of the experience for killing them is lost, as the killers are themselves killed. That gives an average of perhaps 41 x.p. per hit point damage gained in any given battle - or war, as the case may be.
Let us consider the 30 Years War (1618-1648), which ends just 2 years before my campaign begins. Estimates for the number of killed in that war are anywhere from 3 million to 11 million; for my campaign, I prefer the high number to work with (the quibblers are having a field day).
If we assume that an average, untrained human has 4.5 hit points (1 hit die, 1d8 per hit die), this is a total of 51,750,000 hit points killed, minimum. Leveled persons and even men-at-arms have more hit points on average. All told, we can argue the real average in a D&D army would be quite a lot higher than 4.5 ... but let's be conservative and make the number just 50% higher. That gives us a nice round 75 million hit points caused to dead persons. A lot of these wouldn't be combatants - just butchered people in town, given the nature of the war - so we don't want to push those numbers too high.
I have numbers that say the size of the participating armies in the war - at any given time around 1630 - were about 545,000. It's unlikely that many participants were part of the army for the whole 30 years, and NONE of the armed participants from Germany are expressed in those figures. In addition, there were armies of Poland, Hungary, Italy and other smaller entities that took part, as well as one hell of a lot of freelance mercenaries who did not consider themselves part of any army - plundering at will as they went.
Total participants must have been at least 32,000,000 over the period of 30 years ... and since the experience system enables you to gain experience from suffering half your hit points again and again and again, by FAR the greater balance of hit points suffered by any participants in the war would be suffered by those WHO DID NOT DIE.
How many hit points, total, has your 8th level fighter taken in all the campaigns he or she participated in? Ten times your hit points? Fifty times?
In my world, it takes 1000 x.p. for a man-at-arms to become a 1st level fighter; if that man-at-arms gets 4/5ths of his average experience from being damaged, he or she will probably suffer 33 hit points damage to do so (1000 over 0.8 x 41 x.p. average). Non-leveled persons don't get experience for treasure in my world.
Call it a reach; call it silly; call it mental gymnastics in the extreme - you wouldn't be wrong. I titled this post knowing what I was doing. I think it is reasonable, however, to use this number to estimate the total damage suffered by the 32,000,000 participants in the war. No, that number isn't real. NONE of the numbers here are real. But I'm not building a nuclear power plant, so no one's going to die.
All I'm suggesting is a number of hit points that were suffered on account of that war, the Thirty Years War. The number I'm suggesting is 1,056,000,000 total hit points lost by non-dying persons over a period of 30 years. Add the number of hit points of those killed, and round the number down, I have a reasonable figure of 1.1 billion hit points lost. That's 45 billion x.p. - from battle alone. Lord knows how much experience we're talking gained from plunder. Twice as much? Three times as much? More?
Don't let the inaccuracy of the figures disturb you. The real numbers - if we could go back and tally them like bean counters - would certainly produce truly staggering amounts of experience. If we triple the experience gained by taking plunder into account (and plunder was excessive during that war, particularly if we argue that destroying a 1,000 g.p. cross for the good of one's religion is as significant as carrying home coins), we're talking 135 billion x.p. Divided equally among ALL the participants, that's 4,219 each.
But of course you know it wasn't divided equally. The more powerful always get a greater share - and there was enough experience going around to enable more than 1.35 million participants to gain 100,000 experience or more.
So where did all the high levels on this post, in Germany, get their experience? It's not a mystery.