Hi!
The high number of destructive giant raids was something I noticed (I mean, 2,000 raids on a single dwarven hall by the year 600 - you can't be serious). And civilzations extinct - well I have this one world 10 civs setting with 1,600 caves and seven abandoned halls/towns/forest retreats/fortress. No living human,dwarf, elf, or goblin since around the year 120. A good world if you do not want to be bothered by anyone :) :) :)
Anyhow, the reason I responded was to point out something which may be useful for such cases. When you are investigating something like this, get the general info/map generated for the world. In the history file, you get all the civilizations created with their rulers, including the death of these rulers (except for the aristocratic humans). This can give you a hint whether civilizations of the race you want have been created and how many have been created.
With the year of death of the last of the rulers, you can then go into the legends (provided you opted for revealed legends, of course) and then sift through the time around that for the death event of the ruler; probably this will link you to the war or rampage at the core of his/her demise.
Alternatively, you can look for the abandoned sites in the sites file and then see the sites' history in the legends - this way, you can see if there was some pattern to the trouble. Sites are sorted caves first then all else (kobolds are irregular; sometimes they live in the first bunch of caves, sometimes they have an extra cave listed with the towns).
BTW, the sites file lists all inhabitants of a site (only race not name), so it is nice for a quick head count of megabeasts or demons :) :) You can also see whether there are any goblin fortresses actually inhabitated by goblins :) :) :) :)
Deathworks