The First Celestial War

The first violent conflict resulting from the schism between "good" and "evil" gods.
The The Chromatic/Metallic Dragon Conflict began this war, with the two types of dragons starting a battle and the other gods aligning themselves with one side or the other. It ended with all gods who supported Tiamat being labelled "evil" and all those who supported Bahamut being labeled "good" and the two factions being separated into different planes. The few gods who didn't side with either side were labelled "neutral" and were allowed to settle in whatever plane they wished.
This conflict also resulted in the Treaty Name TBD, in which the gods agreed that any future battles between gods would only occur on the Material Plane or would be fought among the warring gods' mortal races rather than in the celestial planes.