The War of the Elves

Taking place shortly after the Fey War, the War of the Elves was a conflict between the elven city-states of the Everglenn. Though short, the war had long-lasted consequences: The "dark elves" - those that wanted to continue attempting to subjugate the other races - were forced to flee the Everglenn, finding sanctuary in the caverns of the Underdark. These elves would go on to become the drow, and would continue to attempt to rule their elven counterparts during the Breaches.

Civil War in the Everglenn
After the Treaty of Izlandar was signed in 5870 BFA, achieving peace with the other races of Baelor after the Fey War, many elves felt that the conflict should've continued, believing themselves to be superior to other races. Unhappy with their new leadership, several city-states succeeded from the rest of the elven nation, attacking their elven compatriots and beginning the war just a year later in 5869 BFA.

The war was brief. The "dark elves" as they would come to be known lacked the resources and numbers of the other elves. Yet the dark elves fought tooth and nail across the Everglenn, often resorting to burning their own cities rather than letting them fall into the hands of the rest of the elves. But as it became clear that they were on the losing side, the dark elves began to plan for their continued survival.

Abandoning their homes on the surface world, the dark elves fled the Everglenn, eventually making their way to the Broken Expanse. Unwilling to pursue their counterparts, the elves of the Everglenn allowed them to escape, focusing their efforts instead on rebuilding their once proud city-states. After reaching the Broken Expanse, the dark elves travelled deep into the canyon, eventually finding their way underground to the Underdark. It was here that they decided to stay, finding a new home beneath the earth.

Aftermath
The War of the Elves, though short, had long-lasting consequences. After thousands of years living in the Underdark, the schism between the elves became permanent: Those who fled underground evolved into the drow, dark-skinned elves that continue to build cities within the Underdark. However, the drow continue to carry the anger of their ancestors: They have attempted three invasions of the Everglenn, in the hope of overthrowing the elves and reclaiming their ancestral home. These events are known as Breaches.