DF player is no stranger to the amusingly terrifying ways to rule your fortress, or even more disturbingly fun things the game itself threw at you.
Well, it seems we got a new one!
So preamble is the following: I've created a world, created few meh-level forts, retired them, founded another one and sticked to it. Years come and pass by, and the news that the liason brings to me become even more upsetting each year: the goblins are coming, and their war-machine is tougher than ever. Settlements and fortresses fall one after another. And one day, the liason told me that among those bastions fallen was the fortress that I've established some time ago.
Of course, what I did next is that I retired the fortress I've been playing and tried to reclaim one of those I had. They were listed as "ruins". I've packed my expedition with warrior dwarves, equipped them as good as it possible, and sent them to bring me back what belonged to my people.
And now the main part: apparently, when the goblins seized the fortress, they decided not to act as homicidal maniacs* and instead of butchering every dwarf there, they've just executed a few, and let others roam freely.
But the Great Dwarven Queen didn't appreciate it. When i appeared at the place, all dwarves that were there (except for mine 7) were listed as "Hostile" - which means that I had to kill them. They weren't attacking me or running away, but still I had to kill them. The FPS dropped quite a bit, as of the game ENGINE itself was urging me to get rid of those pesky inhabitants.
And so I attack.
Well, do you remember that legendary miner you had that has been easily bashing the skulls of goblins/berserkers/whatever? Well, now, that guy won't like you attacking him and will pose a problem for your assault squad.
All in all, even my attempt to kill them in just a massacre ended with 4 of my 7 dwarves dead in a minute. But I killed dozens of civilians.
So, it seems, the locals changed their loyalty after being conquered, and the game regarded them as enemy nation.
And that's what it apparently means: The Monarch of Dwarves won't tolerate even a glimpse of disloyalty and cowardice! Any dwarf that refused to fight till the end against the Enemy and gave up is traitor: no matter is he a civilian or a soldier. Therefore, by the Royal Decree of the Mountain Crown, all dwarven inhabitants of the goblin-conquered forts are subject to the extermination as they are vermin that betrayed their people!
Even as I type this, the voice of Comrade Urist McStalin rings in my head.