A while ago a youtuber (GenJeft) posted his fortress on the DF download site with a link in this forum.
It happened to be an abandoned fortress with the corpses of several sieges laying scattered all over the place. Eventually the fortress was ran over and almost every dwarf killed before it got abandoned. They were also scattered all over the place. On top of that many coffins were empty with their previous contents scattered as well.
My first reclaim attempt went completely wrong. Dwarves got insane after seeing that many corpses.
My second attempt failed because many ghosts started to kill my starting seven, leaving the rest in such bad mental shape that I gave up again.
In my third attempt I immediately started to engrave slabs and took great care of filling every need I could. Then I started to notice something: the thoughts of the dwarves about past events started to change. First they were "horrified to see a goblin die"x 10. Later the messages changed to less extreme thoughts. Now, a couple of years after, some have the "didn't feel anything after seeing a goblin die" thought.
A couple of versions back this was the way to go: induce so much horror they do not care anymore. Now it seems a version of this is still possible, if you counter the negative thoughts with loads and loads of good thoughts.
One of the reasons it might have worked out is the fortress was well established before succumbing to an invasions. All furniture was masterwork. It wasn't too hard to get a lot of positive thoughts.
Maybe related, maybe random, one of my dwarves got caught in a rain and started to love nature. While profanity to dwarven ethics, this treelover did not care about rain after anymore too. If it was not random, it might have had to do with the fortress being entirely lit in the inside because it was constructed in a huge dug hole. Dwarves had zero cave adaptation.
http://dffd.bay12games.com/file.php?id=14432 The great stoneware fort. This is a fun fortress to try stress related issues. Don't be alarmed if your computer freezes while loading the fortress. It takes a while to process the ten thousands of items littering around. After sending them of with a caravan or destroying them right away it becomes playable.