A Shadow over Akeroth
The Aspects came together in Yseria, drained after centuries of constant warfare and watching as countless millions died at the hands of the Chromatic Dragons and their twisted Dragonspawn servants, the Aspects finally decided that they alone could not defeat the Chromatic Dragons and they agreed that the Titans should be brought into the fray. Together using the last of their energy the Aspects called forth the Titan Bahamut (the Titan of the Dragons and the keeper of Order in Akeroth), here they beseeched the Titan to use his powers to seal away the Chromatic Dragons, however, Bahamut responded that he could only do this by using the Aspects Divinity (and therefore their immortality). Faced with the lose of their Divinity or the complete destruction of Akeroth at the hands of the Chromatic Dragons, they willingly gave up their immortality to seal away the Chromatic Dragons.
Bahamut taking the Aspects Divinity sealed away the Chromatic Dragons, however, with this action Bahamut created a complete opposite of himself forming the Chromatic Titan Tiamat; the creation of this duality forced the Titans into an eternal combat that continues to this day. Before the eternal combat began between Bahamut and Tiamat, Bahamut laid an egg which is fabled to return the Divinity to the Aspects if they find it first, however, because of this action the Chromatic Dragons were only sealed away temporarily and when the Cataclysm happened in 12A it released the Chromatic Dragons from their sealing.