Havent played in a while but I thought I was pretty good at this game. Boy did the undead siegers prove me wrong. They not only seem to completely ignore all my traps, waltzing over them like they werent there, the two first that entered the fort also managed to kill everyone. Thats including 20 hammerdwarves with silver warhammers and full iron gear with several proficient. It was just like they were nothing.
To top it off I had no idea they would come since there was no indication that a tower was near when I chose the spot to embark. I thought goblins would be the worst since they were only 1 day away. This was also just after the fourth migration wave, but I dont think undead ever had a check for such things. I guess its back to the old raised bridges turtle strategy again just to prevent this from happening again.
I had the trap thing happen also!
The Steam version has a setting in "labor" where you toggle trap-loading between do always, do never, don't do during invasions.
The default is don't do during invasions. I gues the same thing happened to you - When the invasion came, I built traps. But the default it set to the dwarves not loading them during and invasion, so none of them got loaded. And we don't know the visual difference between a loaded and an unloaded trap, so we couldn't tell.
Like a stone fall trap, the chain is straight up when it's loaded and hanging loose when it isn't. So when you get used to the game, we'll be able to see that none of the traps in the trap hallway are loaded.
If you find that trap settings and get those traps loaded then it's business as usual with that.
IDK about the military though, I haven't figured that out yet haha. I had some marksdwarves beat a zombie to death though, so there' that. Maybe the intelligent undead like sallow walker etc are super strong.