I just had a lot of fun. Not the "Oh crap I'm about to loose my fort" but "Oh crap I might loose my fort but this is very interesting let me watch this."
It all started with a goblin ambush, four macemen and a swordsman. Normally such a force would have been trivial, but only a year in I didn't have a militia besides seven marksmen lacking in any melee combat skills. Resigning myself to a few losses, I station my men in the path of the goblins and immediately bolts start flying. One maceman goes down as they charge, then another, before they crash into my militia.
My Militia Commander/Mayor (almost legendary in crossbow skill) thankfully unloads into the swordsman's face before he gets chopped up. War dogs rush in and distract the other goblins while my crossbowmen continue to pelt them (from two feet away) with bolts. The battle quickly finishes, body total: two marksmen, four dogs, five goblins.
As I order my militia to secure the only way in my fort, the bodies rise from the dead- a second later my screen zooms onto the necromancer likely responsible, standing right next to a dwarven kid. As the kid's head sails off in an arc thanks to the necromancer's knife, his new thralls lay into my marksmen. The game pauses and zooms onto a different area, again, and notifies me that the dwarven caravan has arrived.
Ignoring them for the moment, civilians continue running as my marksmen fall in droves, my Militia Mayor only surviving because he ran out of bolts and I swiftly turned off his military status before he could ineffectually bash them with his wooden crossbow. He, the last member of my militia, falls back to get more bolts as my civilians get torn apart by the growing zombie horde.
Then another ambush appears, right on top of my miners working outside the fort! They scatter, the lower level ones rushing into the fort while my two legendaries lead the goblins on a merry chase through the forest. Anxiety welled up in me as I watched the goblins close in on them, only to deflate when the miners kneecapped them whenever they got too close. Somehow, this didn't send a hint to the attacking goblins so they continued crawling and eventually trapped my miners in a dead end.
Leaving them to their suicide, I zoom back to my fort just in time to see the dwarf caravan enter. The guards immediately rush to fight the zombies while the merchants dither about the gate, walking in only to see the zombie horde, running out in terror, then immediately walking back in because they forgot about the zombies. Knowing that they'd easily fall with the necromancer still alive, I set my commander to kill him.
In the time it takes for him to arrive, two guards fall and join the nudist horde. He shoots a single bolt, the necromancer drops dead, and from there the remaining guards slaughter the undead. Now I just need to deal with the tantrum spiral that will soon commence.
TLDR: Necromancers make things very fucking interesting.