Celebrim
Legend
Sure it is relevant. When there are no heroes present the armies rule. You seem to think that heroes are everywhere.
No, I don't. I think that, under certain D&D demographics, its not relevant whether an army is present. The locals will just shrug and say, "Yeah, you could kill us, but then you'd have to answer to the heroes when they inevitably come along."
The real problem here is that you are preexisting the existance and concept of an army in a world where the fundamental laws of the universe make such a concept improbable. It's like answering a question about this world with, "Ahhh, yes.. but magic." Start with the assumption that the world is filled with heroes and postulate the successful creation of an army.
Bad thing is, in most settings those are rare...
First of all, we aren't dealing with 'most settings'. We are examining the consequences of a world where victory goes to the brave rather than the bigger batallions. So we can dispense with discussing all the worlds where that isn't true and save them for a different thread of conversation. And secondly, it is not true that 'most settings' have heroes 'rare'. Most published D&D demographics and most published D&D campaigns have heroes sufficiently common that it is not explained why armies exist. FR is an example, and there are several others, and I note that FR at least tries to explain it by having average members of armies be 4th-6th level fighters (which produces its own problems with the settings internal logic).
No, without garrisons you can't rule anything.
Sure you can. There aren't garrisons in most villages, towns or cities either now in the modern era or especially in middle ages. In the middle ages, the era from which we draw the myth this 'victory to the brave not the battlions' is drawn on, there are real parallels to this world without armies. For one thing, there was almost no such thing as a standing professional army. Moreover, it's not usual to keep the peace with your standing army. You don't need garrisons to rule, and arguably, during the middle ages, the peasant class didn't care who was in charge so long as they respected thier historical priveledges and kept the taxes at the same rate. Wars were for nobles (heroes); it was the very basis of noble priviledge that they would protect the peasant class and keep them out of their squabbles. Peasants barely participated in wars as such.
How to make sure that the conquered village/town is actually doing what you want?
You don't generally care what they are doing so long as when your tax collector comes around they pay up. So all you really need is the aforementioned armed bureacrats. If some towns gives the armed bureacrats trouble, he just says, "Pay up or I'll summon my Lord, and you know what sort of trouble that will mean."
Keep a hero in every town?
In sense, "Yes." You enfuedate every hero whose allegiance you can muster and distribute them around the kingdom as point defense.
Then you hardly have heroes left and have to rely on armies.
Your logic does not follow. You basic problem here is that you are trying not to have the world work according to the premise, because you don't like the consequences of the premise. I can't be blamed for that, but I assure you that it is quite easy to reach the world of the premise via the D&D rules set.
So you just send some heroes with the army. Army + heroes > lone heroes.
Not necessarily. Crowd of toddlers + band of heroes < band of heroes. The problem you get into is that at some level 'n', ordinary soldiers are not only no longer relevant, but because of the supply problems that they represent, because of their visibility and lack of stealth, because they represent extreme threat to themselves and their allies if someone bounces a ball with a Symbol of Confusion into their midst, and so forth the army actually becomes a serious liability. If 'n' level characters exist in any numbers, then the army becomes just a way to get a lot of your citizens killed and make your people demoralized.
In WW2 infantry was, at least in the beginning, pretty useless against tanks and aircrafts. But did nations stop using infantry?
Bad analogy. We know that the real world generally favors big battalions both by observation and the fact that we know it doesn't have superheroes in it.
You run a very strange game.
I didn't run that game. I run a gritty game. I was a PC in that game. It was strange, but it was an interesting change of pace from my normal fare. And yes, it started out with armies and all the other assumptions in it, but it pretty quickly became clear that with high end D&D PC's (and NPC's) armies were mostly decorative unless you did some rules alteration.
Cut that (by destroying the mines, etc) and even they get problems. And break their magic stuff and they have a hard time getting it back.
Sure, but the problem with all this guerilla warfare stuff is that the heroes just do it better. Destroy the mines? "Hmm... I teleport without error to the mines, summon a greater earth elemental, and order it to dig up some diamonds. Ok, now I cast a divinition of some sort to find out how annoyed me, teleport there and cast a Storm of Vengence to kill the entire rebel army. Then I'll summon up a few Invisible Stalkers and order them to paint "Thus it happens to any that thwart Lord V." on the walls of the dead men's homes in the blood of their families." (Or some variant thereof.) Break their stuff? Get real. First level characters don't have anything that could break a +5 sword even if they could get a hold of it.
First level characters don't mess with high level characters. And in any world where high level characters exist, they would have learned that long long time ago.
Also what are the enemies 17th level heroes doing? They can fortify a place like heck. So, siege.
Do you know what the word 'siege' means? It doesn't mean merely assaulting a fortified place.