Zasit Fikodas, captain of the Earthentop fortress guard, felt completely helpless. His fortress, the one he had sworn to protect, was falling apart around him. He traced the scar along his belly as he had come to do frequently over the past weeks. It had started so quickly. It didn't seem right for it to be ending so slowly.
He had been there when it happened - some goblins were sieging the fortress. Not an extraordinary situation, but it appeared that the dwarven caravan would have to bypass the fortress that year if the siege went on for much longer. So the decision was made to lower the drawbridge over the magma moat, allow the goblins to be weakened on the traps as they tried to enter the fortress, then have the military finish off the crippled ones.
It didn't quite work out that way. A group of trolls charged in first and were finished off quickly, but some overzealous soldiers had charged out to meet them on the bridge and three of those were knocked into the magma. The soldiers regrouped as a squad of macegoblins attacked, and finished that with one or two losses. Then a squad of speargoblins led by the goblin swordmaster Bosa Ngusluoga made their way across the traps mostly unharmed, mainly due to the bodies of their fallen allies clogging them. A group of dwarves had come out to clean the traps, and Bosa appeared to have a plan. He danced through the dwarven squad and went straight for the civilians, slaying the mayor. He was mobbed by four soldiers and killed soon after.
The remaining goblins retreated. It was a victory for the dwarves - ten dwarven deaths (3 civilians, 7 soldiers) for about twenty goblins and half a dozen trolls. Zasit himself had killed enough goblins to be honored with the title Legassolam Momuz, "The Lush Nation of Crypts". But the mayor was a popular dwarf, with many friends throughout the fortress. So it was no surprise when the first dwarves went berserk.
The weeks that followed were chaotic. Tantrums happened constantly. The jail filled up within a couple days, leaving Zasit with only beatings to give. This only made the population angrier, and dozens of dwarves either fell into depression or madness.
It was at this point that Zasit sat in his room and traced over his scar with his hand. He was worried for many things - his lover Meng Rithmothdast, the berserk dwarf locked in his room down the hallway, and would that sobbing dwarf outside his room just stop sobbing he had been hearing their wailing for weeks now. It was at this point that his vision turned red, and Zasit Fikodas did not feel helpless anymore.
Chaotic visions danced before his eyes. His mace ended a dozen dwarves, many of them just looking up at him with empty eyes as he caved their skulls in. Some struggled, but he chased them down. After all, he was the best trained dwarf in the fortress. He made his way from the bedrooms to the meeting hall and killed another seven. As he left the area, he heard something from the hospital.
His vision cleared momentarily as he saw his lover, Meng the cheese maker, step out of a doorway and face him. Then, as if he was looking in a mirror, Zasit saw her face turn into one of pure rage. His vision darkened and then he was looking down at her body. Something had killed her - his future wife! The red around the edge of his vision crept towards the center, and he didn't fight it. His shouts of anger turned into a continuous, wordless battle cry as he charged down another hallway.
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Tantrum spirals are scary. Zasit here basically rampaged through the fortress, killing everything he saw, until a fleeing child lead him over some traps that eviscerated him. He killed four goblins in the initial fight, and then he killed forty seven dwarves. Some of these were beatings, yeah. But out of a fortress of 162 before the spiral, he killed over 25% of the population, and most of that was while berserk.
Moral of the story: make sure all your military dwarves can handle stress.