Back to whether this a belief/cultural/racial conflict.
Part of the problem for us as 'connoisseur' readers in this, is that, because we mostly see metamorphorical Discworld Trolls in A-M in the 'lowlands', we also see them in a much different light to how they are up in the mountains. We all know that Trolls are severely impaired in hot climates and so we don't
see them in places like Genua, a delta city on semi-tropical swampland, or at all in Djelibeybi or Omnia which are largely desert as Trolls wouldn't go anywhere near those places, unless there was a v. good reason (and therefore why we only see Detritus in Klatch during Jingo
and in a terrible state during the day of course). As I say - we know this, but
actually we very rarely see Trolls in their natural home ranges in the books.
I can just about recall 1 encounter in the Witch series, which was either in WS or L&L and a toll bridge was involved.
The only other instance (so far as my mashed brain can remember), where we see Trolls in cooler mountainous territories, which of course suit them very well indeed, is right back in LF where we see a more 'traditional' fantasy fiction troll clan living nocturnally in a temperate area, not mega bright, but pretty much on the ball and, in the elderly (Grandpa) reverting more and more to their natural silicous state as they grow tired of life amongst the pretty oograh and come to resemble the rocks they live amongst.
Wiki is fairly helpful on troll culture
(see Wiki - Troll (Discworld)) in the later books and in the first sentence says that they have many gods
. So from this PoV, belief does
play a big part in the Trolls
many conflicts with the Dwarves, who are not exactly godless, but do have other motivations which I'll come back to in a mo. However, I disagree that Koom Valley is 'simply' a rallying symbol of opposed ideological factors - is more fundamental (in a non- religious manner) and much simpler than that.
Dwarves love to mine for ore etc and so they are attracted to the same kind of territories that are inhabited by Trolls, who choose to live there purely because that type of climate and landscape is their natural habitat...
Dwarves burrow and delve into the mountains and bedrock
Trolls live in mountains and bedrock
This is not
about belief, or even race as such - this is
about conflicting territorial and cultural clashes
How would you like a bunch of determined little squirts bashing your bedroom wall down, just to get at a promising vein of copper or whatever. Or excavating a nice piece of quartz (even if it does clog the arteries) in your larder that you fancied for your supper...
Koom Valley is like a metaphorical rainforest with the Dwarves as the tree-fellers and the Trolls are the indigenous natives who are defending their ancestral territories and literally their lifestyle
Thud is gang 'turf' warfare taken too far - it's all about rock and how each faction wants to use it, where the Dwarves are the invaders and the Trolls are the eco-warriors