The Great Divide
In accordance with The Pact Primeval Asmodeus was able to continue using the souls of mortals to continue gaining power and influence. His power became so great using his method that in a very short time he would be able to threaten, and even overtake, the power of the gods. Going back on the agreement, some of the deities (whose identities are speculated on even today) got together and decided to subdue Asmodeus and chain him up in the lowest level of hell at the base of his palace Malsheem (Planar Handbook p 123). From there he was able to appear to the other denizens of hell through masterful use of the project image spell while he bides his time and planned how to enforce justice once he broke free. The other devils DID NOT know about him being bound, for if that information were to come to them, all hell truly would break loose. It is so great a secret that it does not the truth does not even exist as a rumor in the Nine Hells. In fact if it is voiced in the Nine Hells, the Aspect of Asmodeus is instantly drawn to the location and centuries of torture prove that he is both powerful and conscious to the individual that dared utter such a sentence.
When Asmodeus was freed (no matter who actually assisted with the endeavor) we know that he spent very little time in bringing to light what had occurred. His declaration immediately caused the deities to begin taking sides. The term “Great Divide” stems from the fact that even gods who were once very close in ideology immediately and irreversibly parted ways. Some Lawful Good deities saw Asmodeus’ imprisonment as unlawful and joined sides with him to punish those who broke the law. Some Lawful Evil deities agreed that Asmodeus’ imprisonment was justified because of the way he openly perverted Law to gain personal power, and sided against him. Some Chaotic deities did not want to see justice done, and therefore took the side against Asmodeus, while some Chaotic deities reveled at the amusement of battling Lawful deities under the banner of Law and sided with him. Using just a few examples, it is easy to see how this matter got out of hand.
The success of the war has been shrouded in mystery and bloodshed. The only thing that historians agree on is that the war is over. With so much violence, many of the planes had been drastically altered into a ruined landscape. The indigenous people of many planes fled in order to avoid the conflict, and remnants of this can be seen now where it is not uncommon to see Tieflings born in Bytopia, or Aasamars in Hades.
Despite what many choose to believe, a vast number of deities are dead (or at the very least powerless). This has not had a noticeable effect on the faith lives of many clerics who still believe their god to be alive. Without hard evidence of death, it is impossible to tell the status of a deity. Athar philosophers are quick to point out that spells are still obtained because it is the faith of an individual that brings power, not the entity that calls itself a god.
Relation with Taint
It is important to note that Taint began appearing around the time of The Great Divide and is keyed into the discussion of the topic. There are theories that Taint was manufactured my Asmodeus in order to drastically increase his power as more souls succumbed to depravity and evil. If these are to be believed, then the origin of Taint is a biological weapon that the armies of Asmodeus deliberately spread in order to aid them in their war.