Age of Darkness

The Age of Darkness was a thousand-year period in which the sun's light was blocked by the ash knocked into the atmosphere by the meteoric impacts of Earthfall. It began with the impact of the Starstone and lasted until the sun's light had been restored. During the Age of Darkness, all major civilizations across Golarion were destroyed, ushering in a time of anarchy and destruction.

Fall of Empires
The thousand-year darkness that blanketed Golarion destroyed the remnants of most of the existing civilizations that had risen during the Age of Legend, including the human empires of Azlant and Thassilon, and the already fading cyclops culture of Ghol-Gan.

Emergence of races
The Orcs emerged on the surface from their Darklands homes, fleeing the Dwarves pressing up during their Quest for Sky. The darkness also beckoned to the Wayang from the Plane of Shadow, who began immigrating to the continent of Tian Xia during this time.

Return of Zon-Kuthon
The god Abadar had banished Zon-Kuthon to the Plane of Shadow long ago, not wishing to destroy him completely, but had created a loophole: Zon-Kuthon's exile would last "as long as the sun hung in the sky". The dark god took the darkness on Golarion as the fulfillment of this agreement and returned from exile to wreak more misery on the world.