Scattered War

Not quite 500 years after the Divergence, Warren Drassig rose to power in Emon, established the Kingdom of Drassig, severed diplomatic ties with Syngorn, and made new alliances with Kraghammer. Yenlara's grandson, Syngorn's diplomat to Emon, tried to resolve things diplomatically, but was tortured and killed, kicking off the 32-year Scattered War. The elves of Syngorn established the hidden Emerald Outpost to keep watch on the growing Kingdom of Drassig. Within the next nine years, the port city of O'noa was devastated in one of the bloodiest battles of the war.
When Warren Drassig was ambushed and killed at the village of Torthil, his son Neminar succeeded him and made a pact with Bane to fuel his war effort. A human rebel named Zan Tal'Dorei later drew Neminar into the Verdant Expanse and killed him there, at which point Neminar's brother Trist Drassig took command of the kingdom.
Zan scored a series of victories against Trist, forcing his forces into a valley at the base of the Cliffkeep Mountains, but as Trist had made yet another pact—this one with the Demon Prince Graz'zt who had once made the nearby Grey Valley a bastion of his influence—a flood of fiends poured into the battlefield. Against all odds, Zan Tal'Dorei's forces prevailed, ending the Drassig bloodline, the infernal pact the Drassigs had made, and the Scattered War. The blood of the demons thereafter blackened the grass and flowers that grow there, and the area became known as the Umbra Hills. The leaders of the Verdant Expanse convened a council, crowned Zan Tal'Dorei as Sovereign in a power-sharing arrangement, and named the realm Tal'Dorei in her honor.