Arkhandus, you bring up valid points, and I will adress them.
Arkhandus said:
Uh, y'know the DMG already has guidelines for that, right?
I know.
Arkhandus said:
A metropolis, like Rome or somesuch, would typically have 4 wizards of 13th-16th level, 4 sorcerers of the same level range, 4 clerics of 13th-18th level, and 4 druids of 13th-18th level. Along with 8 members of each of those classes ranging from 6th-8th level (9th max for the priest types). And several times more of much lower level.
Metropolises aren't likely to be found in every kingdom or region, however. Most cities will have only 2 individuals of each major spellcasting class ranging from 7th-10th level or 7th-12th level, and 4 individuals of 3rd-6th level in each of those classes, and maybe a dozen of lower level. Towns and villages would only tend to have a 1st-4th level spellcaster of each class, maybe a 7th-level one in the bigger towns. If they have any spellcasters at all.
Fine, this is what the DMG says. Summary:
Metropolis: ~8 arcane casters capable of Teleporting
Large city: ~6 arcane casters capable of Teleporting
Small city: ~2 arcane casters capable of Teleporting
Arkhandus said:
So in the biggest cities of the world, which are likely to be countable on one hand or two maybe, you could expect to have 8 folks capable of 5th-level arcane spells (like Teleport, but it's less likely that the 4 highest sorcerers in town all know that spell), and another 8 folks capable of 5th-level divine spells (like Raise Dead, but that's only for the 4 highest clerics, not the 4 highest druids in town).
This is where I think you oversimplify. The chance that a town is a small city or bigger is 15% (DMG table 5-2). This makes me believe that there is a lot of small cities, and hence a lot of Teleporting-spellcasters.
Arkhandus said:
If one of those metropolises went to war with another, they might be able to teleport a few assassins into each other's territory each day, with some margin of error, and may be able to use limited high-level-spellcasting tactics in their war. But they'd be able to get their leaders Raised from the dead anyway, probably,
Sure, Raising from dead is one option, but it costs far more than the attack itself. In addition, the raised leader is less powerful (-1 level). So the attackers win big time.
Also, if the leader is somehow prevented from being raised (if kidnapped, disappeared,etc), a power vacuum is likely to occur, in which opposing sides fight for their rights. Again, attackers win.
Arkhandus said:
so the clash of armies would still be an important deciding factor in their war,
Indeed, the clash of armies will still be important. But the hit-and-run possibilities that high level spells introduce may be an important asset before it comes to the clashing of armies.
Arkhandus said:
and the few major spellcasters on each side would be kept busy with just trying to counteract the biggest spells the other side's major spellcasters were using for espionage, infiltration, and destruction.
I disagree. Trying to counter the opposing moves is a definitive suboptimal solution in D&D. Creating a defense for any possible attack requires far more resources than attacking.
Arkhandus said:
Whereas a moderately larger number of cities would be lucky to have access to a single spellcaster who knows Teleport and has 1-3 spell slots for it each day, or a single cleric who knows Raise Dead, or a single druid who knows Reincarnate.
And that stuff's only if using the DMG's guideline for communities, since it's only there as an optional guideline to begin with.
I know it is just a guideline. However, with these guidelines, I disagree in how the DMG presents the world with all these high level spellcasters. IMO, it should be very different from the one presented by the DMG (ex. no diseases, like you mentioned).
Moreover, I have the impression that most gaming groups and published adventures assume more higher level NPCs than the guidelines suggest.
Sorry for being off topic. Hopefully Obergnom already has enough feedback to make a decision.