Ash: Rise of the Republic

2015: The Yellowstone caldera tears itself apart in an explosive eruption an order of magnitude larger than expected. More than ten thousand cubic kilometers of ejecta are thrown clear the first day. A boiling pillar of vaporized rock, thirty miles high, towers over the continent. Within hours, the ash begins to fall. Within days, millions are dead. Within weeks, the government has fallen.

2045: After struggling to survive thirty years of volcanic winter, a small city-state in the ash fields of Central Texas has begun to flourish. Founded in the ruins of a major university, fueled by technological innovation, and protected by roaming companies of hardened rangers, the Republic is on its way to becoming the dominant power in the region. Its factories and farms have restored a measure of relative peace and stability to the scattered remnants of humanity. Trade is thriving, people are eating, and civilization is finally something more than an old story told around the campfire.
The fragile peace is shattered one night when a valuable fuel shipment is destroyed on a deserted stretch of highway. The rangers are summoned, but they soon find that this is no ordinary outlaw raid: a new menace is brewing in the wastelands.