War of Wrath
The War of Wrath began as soon as the War of Arcanum had nearly ended. Before the War of Arcanum raged, Teritus , Zaridun and Torog had been scheming of a way to return to the material plane and claim it for themselves, as they grew tired of the beauty and grace of the outer planes. It is rumored in the most remote and storied libraries that Zaridun himself is said to have instigated the Magi into challenging the gods, thus causing the War of Arcanum. They used this excuse to build up their forces on the material plane, and gather followers of great power to their side, all the while convincing their siblings Talos, Bane , Myrkul , Lolth , and Malar to join them. They used their siblings as a distraction, and when the war of wrath first broke out, it had pitted almost all the gods forces against each other.
It raged for nearly a month before the corrupted Slann, still fighting the War of Arcanum let loose a rogue spell that opened the divine gate just long enough to allow Zaridun, Torog, and Teritus to slip through. Demons poured out from the hatcheries constructed by the Traitors, overpowering the forces of the Lost and the Prime. When the Lost Gods realized what had happened they, turned on their siblings, trapping them behind the arcane gate with the Prime Deities. Some, like Talos saw the error in their ways immediately, and sought for redemption by joining the fight against the traitors. Others hid themselves away in shame, angry at the prime deities for trapping them away. At the end, for one reason or another, they all dedicated themselves to the cause against the Traitor Gods.
If not for the actions of Asmodeus, an angel who had followed Torog through the divine gate as her commander, the war might have been lost, and the material plane might more closely resemble the Abyss. For he turned his back on Torog and conducted a powerful arcane ritual with the remaining magni of the Arcane cities, and brought into existence the powerful devils, who rivaled the power of the demons.
While Asmodeus held the demon forces at bay, it was the mortal Torm, The Enduring Hand who ushered the forces of the prime to make one final allied battle, and banished the Traitor Gods into the newly prison plane, The Abyss. The resulting event led to the Calamity.
Thus the war had ended, and Asmodeus, who began the war as a mere angel, was risen to the status of godhood, and given command over the devil armies he created, and tasked with permanently keeping the Traitor Gods and their demons at bay. Torm was also raised to godhood, a champion of mortals all around.