Somewhere around the 2556th season after Snowspine-Crack, the tribe known as Brothon began migrating from their lands near the far eastern plain, generally southeast. The Brothon, whose khiulnter form resembled a rather canine armadillo, claimed that their lands were not producing enough food to feed the tribe (which was evidently true). They were not able to find a satisfactory residence, constantly skirting other tribes' lands, until they reached a place on the eastern coast, north of the snow-capped mountains -- and decided to settle there, having few other options. Unfortunately, another tribe, the Sad'riga, had just chosen to settle there. The Sad'riga, whose khiulnter was a curiously scaled avian form, had no intentions of leaving, their own former lands recently having succumbed to sinkholes and erosion (a rather specialized tribe, the Sad'riga had very few environments in which they could thrive -- the seacoast was the only option for them).
A meeting between the two tribes' elders was sabotaged by an ambush of young hot-blooded Sad'riga warriors, and most of the elders of both tribes were slain. The tribes then went to war, combatting each other with a bloody single-mindedness and ferocity such that other tribes nearby stayed well clear of the conflict.
Slowly but surely, it became clear that the Brothon were winning the conflict. Their armored forms suited them well for long-term battle, as well as their armored mobile fortress, called the Brothos. The Brothos was a curious invention, used by the Brothon and scorned by most other tribes for ages; it looked like a large-scale Brothon warrior, armored and enclosed, and served as a central living area for the Brothon when they travelled and when they settled. It was designed to house most of the tribe, and was utterly defensible. The Sad'riga were effective with their hit and run tactics, but had their nests destroyed with appalling frequency by the titanic Brothos. As the Sad'riga's nests took much time and effort to build, they suffered greatly. Finally, in a desperate manuever, the few Sad'riga left ambushed the Brothos and trapped it, rendering it immobile. When the Brothon took refuge inside it, the Sad'riga sealed it from the outside, and used their sha'crin to burn it from the inside out. The Brothon inside all burned to death; but they had their revenge, for while the remaining Sad'riga warriors danced to their victory outside the burning Brothos, it exploded, laying waste to the Sad'riga and the lands both tribes had fought to the death for.
Those two tribes were wiped out that day. A few of each escaped, but the tribes themselves quickly died out -- a few being executed by other tribes for the worst Crinos crime: Laying waste to the land. As appalling as their crimes were, they were immortalized by the naming of the season in which Brothos Burned, the land was tormented, and two tribes died the final death.