Ursino Sapiens
Nuclear winter is such a bummer. I mean, here you are, a regular bear, living up in the northernmost reaches of North America- not a high-priority target for nuclear strikes at all-, and then all of a sudden it starts raining radioactive dust and all the plantlife is dead from a lack of sunlight. So, what do you do? Well, you could hibernate to try and wait it out- good luck with that. Or you could migrate south. Waaay south. There'll be a bunch of other animals migrating alongside you, but you're the biggest and meanest of them, so they're just free food.
Unfortunately, further south, while not as completely frozen, is even more radioactive. But you're a bear, you don't know that. All you know is, this valley is great. There's a bunch of weird caves full of food wrapped in slices of wood or shiny rocks, there's a river flowing into this convenient crater lake, and nothing in the area can compete with you, because you're a stonking grizzly. You and your fellow bears will make a home here, surviving off of bunkers full of rations, radioactive water, and the occasional animal that wanders into your domain.
Until one day, many generations later, one of your descendants looks at a discarded bone for a while, then picks it up and uses it to hit another bear. Congratulations, you've just attained sapience, as demonstrated by the twin traits of tool use and completely pointless violence against your fellow bear!
Ursino Sapiens originated as a species in a highly radioactive valley somewhere in the north of the Shattered Coast. Rapid mutations led to increased intelligence, and regular bear-competition-for-territory turned into tribal-war-for-vengeance-over-the-last-war. Successive groups of Bearfolk were driven out of the valley by constant warfare, colonising the surrounding valleys- where they also fought amongst each other, leading to more refugees colonising more valleys, on and on until the Bearfolk were ubiquitous throughout the area.
At some point, the very basic tribal society evolved into a slightly more complex tribal society. Tribes began to dominate entire valleys, and- seeking an outlet for their warlike instincts- invade neighbouring valleys. The Bearfolk also developed basic agriculture in this period, although hunting and foraging remained the preferred means of obtaining food.
The tribal or stone-age era ended when some enterprising bear made themselves a crude helmet and cuirass from metal scrap. When other bears realised that neither claw nor simple weapon could pierce this armour, rendering the wearer almost invincible, Bearfolk warfare- and society- changed forever. Suddenly, every bear worth their salt had a suit of hand-crafted armour. The bear with the best armour became the chief- on account of being able to defeat the previous chief in battle. Weaponry advanced rapidly to counteract the armour, with precision piercing weapons and prosthetic claws being favoured for their ability to target weak points in armour. The greatest chiefs managed to unite several valleys under their rule, and had forts built to celebrate their dominance.
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Gliderock
Also known as 'Eternal Ice', Gliderock is neither rock nor ice- it is a metallic substance found in large quantities around the Bearfolk territory. At a glance, it is just regular metal, white with a slight bluish tint- softer than iron, harder to work than gold or silver, it was of little interest to early Bearfolk metallurgists. That was until it was discovered that Gliderock, properly heated and treated, could be brought to a point of almost zero friction.
The earliest use for Gliderock was in sleds, used to transport materials between forts. In this usage, bars of Gliderock were made as frictionless as possible, then nailed onto the underside of wooden platforms. By slanting the front of the bars upwards, the Gliderock sled was able to traverse almost any terrain. Gliderock sleds predated the use of wheels for transport, and Bearfolk society would not adopt wheels in this capacity for a very long time.
Metallurgists discovered that Gliderock could have its frictive properties modified in almost endless ways- it was even feasible for a piece to have no friction in one direction, and high friction in a different one. However, exploiting these properties would have to wait for more advanced craftsbearship, as it was hard to achieve reliable results with the crude forging techniques employed by early Bearfolk society.
TLDR: Armoured bears, metal with adjustable friction.
Upsides of being an armoured bear: strong enough to tear lesser creatures apart, while wearing metal armour thick enough to stop (or at least slow) modern bullets. Downsides: big target, somewhat lower finesse (claws less suited for precision than fingers).
Cultural features: heavy armour, personal combat.