The Sacrifice of the Couatl's and War's End

Era beginning/end

"The war was against an enemy that could not be undone, even by our strength. However, through his insights into the prophecy Hezcalipa saw what must be done, and the cost of it all. In order to defeat the demons and bind them for all time, the sacrifice required would be great, and only he and his people could bear it."
Draconic Histories: The Age of Demons

Couatls sacrifice most of their number to send the most powerful of the demon lords and the majority of the fiends back to Khyber, where they are trapped for eternity. The dragons retreat to Argonnessen to contemplate the Prophecy, ignoring the “lesser races.”