Elven biology/physiology *Possible Spoilers*

It's hard to say with any certainty, for sure. We can figure out some very rough dates for Elvhen war history based on the WoT timeline and what we learned about the ancient elves from Abelas and in the Trespasser DLC. And I don't think it's impossible that the civil war started long before the Veil was raised, or that there were a chain of civil wars that broke the back of Elvhenan, leading to its complete downfall in that last skirmish with the Tevinter Imperium.

-4600 Ancient is supposedly when the elves made first contact with the dwarves. Presumably not long after that is when Mythal and Solas did whatever they did to the Titans and dwarves. Did that start a/the civil war? Maybe, if the other Evanuris thought that access to lyrium would give Mythal and Solas an edge over them.

-3100 Ancient is supposedly when humans arrived in Thedas, but scholars rightly ask where they came from and why they left that place. A largely unfounded speculation I have about this is...  Ghilan'nain apparently was a bit of a mad scientist, and enjoyed creating new lifeforms. Were humans a lifeform she made as soldiers to fight for the Evanuris during a/the civil war?

-2850 Ancient is supposedly when the elves noticed the quickening, which Solas told us was due to the Veil being raised, not to the arrival of humans. So presumably Mythal had been murdered by this point, prompting Solas to raise the Veil. But what we don't know is whether previously immortal Elvhen would have noticed that they were aging and dying immediately, or if there would have been a lag of decades or centuries between the Veil being raised and their immortality being lost. At any rate, Mythal's death and locking away the other Evanuris, not to mention the Fade, behind the Veil created chaos in Elvhenan, according to the Archivists and books in the Vir Dirthara, and Solas himself - it's not unrealistic to think that the different factions, now leaderless thanks to Solas, began fighting amongst themselves for primacy as remaining Elvhen tried to replace the lost Evanuris.

-981 Ancient is when open war broke out between the Tevinter Imperium and Arlathan, and 6 years later is when Arlathan fell, sinking into the earth (because of Titans?). But Abelas tells us that the Elvhen were already weakened by infighting, that the Tevinters were only preying on what was already for all intents and purposes, a dead empire.

So... there could have been one long war that never really got put to rest over the course of more than 3600 years, or there could have been a sequence of conflicts that wore the Empire down over time.