Fiendish Codex I (p. 105 and onwards) details the war at the start of the multiverse between the forces of Law (all of the gods and their servants) against the forces of Chaos (the obyrith and their tanar'ri hordes). Things are rather clear-cut, with the rise of the Queen of Chaos, the imprisonment of Miska the Wolf-Spider, the tanar'ri rebellion against the obyrith and their subsequent destruction/exile, the quick stalemate afterwards followed by the start of the Blood War.
But before the rebellions started Queen Morwel of the eladrin started to wage war on the demons in an attempt to destroy the forces of the Queen of Chaos. The eladrin, while Good aligned, are also Chaotic. But where did they come from? From what I understand this conflict was against Law and Chaos. And I have read somewhere (can't find it right now) that eventually there was a split between the Good and Evil deities, who while all Lawful had their own ideas on what Lawfulness was. So where did the eladrin (and other non-evil Chaotic Outsiders) come from? Were they somehow split off from the Good aligned celestials? Are they some type of offshoot from a proto-Demon form? Or are they something else entirely? I have tried the Fiendish Codexes, the Manual of the Planes, the Book of Exalted Deeds and a few others, but nothing answers this question.