Oh, wow, reading this history is so much fun.
I have mods in for Frost Giants, Orcs, Bugbears, and Hobgoblins. Mine aren't exactly like the ones posted for download, but they derive from those. I decided to regen a world I played before, without added civs, with the new civs. I also decided to run the gen for 500 years before checking the megabeasts because I wanted lots of interaction between the civs.
I started looking at the Dwarven civs, both for surviving ones and also for ones that have a good continuity in the royal line. I've played around with settling a couple of Dwarven ruins (using Embark Anywhere) but regardless I like to start from a civ that has a healthy royal line including either an unmarried monarch or one who isn't widowed/widowered. In other words, I want the potential for a royal baby factory in my fortress.
Anyway, one of my Dwarven civs in this world has a discontinuity in the royal succession that I was unable to understand because there were still four children alive when the previous ruler died. I started digging in Legends, and what I found was that all four children had been kidnapped by Frost Giants. The youngest, a daughter, actually escaped once and was reunited with her parents, but was kidnapped a second time by the same Frost Giant. At that point she gave up and settled into the Frost Giant culture who had kidnapped her.
In looking more closely, I found that three of those four kidnapped children had married other Dwarves and had children within their captor's civilization. I switched over to the world sites and pops list, and starting looking for Dwarves living in other cultures. I found that, over 500 years, some settlements had been nearly replaced by their kidnapped races. For instance, one Orc-founded and Orc-ruled Dark Fortress consists of 41 Dwarves, 33 Humans, 9 Orcs, and 6 prisoners of the first two races. The history of the fortress is filled with kidnappings, counter-kidnappings, and murders, first mostly committed by Orcs, and finally committed mostly by Humans and Dwarves.
Other sites have evidentally been conquered, and some have histories of being passed back and forth between Dwarves, Bugbears, and Hobgoblins.
All this enjoyment and I haven't even settled a site.