The Infernal Insurrection (sometimes referred to as the Third Infernal Emergence) refers a period of chaos, between 925 PR and 943 PR, throughout the Ten Hells and the lower outer planes after the River Styx dried up. Most notably it involved a war between the Ten Hells and Mt. Celestia, destabilization throughout ever layer of the Ten Hells, and the disappearance of Demons and the Abyss. While the River Styx was replaced by the Passage of Souls in 926 PR, there were still many small pockets of instability left throughout the lower planes.
The Loss of the River Styx
The Disappearance of the Abyss
Chaos in the Hells
Gehena War Profiteering
The Invasion of the Material Plane
The Invasion of the Ten Hells
The Emergence of the Shattered Mountain
The Creation of the Passage of Souls
The Destruction of the Ruby Rod
The Years of Fiendish Blood