Which monster from the game is the most dangerous? The dragon you say? The bronze colossus? Maybe the carp? Bah! It's all nothing. No megabeast could waste an entire fortress in less than one season. Fear the king of the monsterkind! Dread the emperor of subtle cruelty. Tremble before the...
...rock gnome.
I decided to make another fortress. I have found a nice spot: a desert neighboring the mountains. Untamed wilds and joyful wilds. That seemed like a good place to settle. It had coal, iron, flux, sand - everything I needed. What it did not have, was a brook... but hey, who needs it? It's not like dwarves prefer water over booze.
So I settled down. I made some workshops and the barracks. My hunter was bringing so much meat I didn't even have to rely on plump helmets farm. I have built it though... I needed booze.
Then the caravan appeared. I had more than enough crappy leather and bone crafts to show them. It seemed logical to trade it for some more bewerages. I bought so much that I did not have to worry even when the migrants came.
My only mistake was not bringing the food inside.
When I realized what's going on it had been too late. The gnomes had gurgled almost everything. My dwarves were trapped on a desert with nothing to drink. But I had a still. And plump helmets. Yay!
Not so much. There's no trees on a desert and the caravan brought about five logs. And every barrel I made was instantly claimed. My dwarves were going to die from thirst, but they could not let this meat and fat lay on the sand. It's unhealthy! No, it was nessesary to stuff these precious barrels with remains of dead animals. If it meant death, fine. Ordnung muss sein!
I tried everything. Forbidding and reclaiming didn't work. I were just using up the precious iron and coal. Every barrel I made, however, instantly was assigned to the food stockpile...
Everyone died.
A lesson: you don't need a megabeast nor an army of goblins. A bunch of gnomes can destroy your city much faster.