The Aetherii was an ancient elven empire that spanned the entirety of Aevira for centuries. Scholars call this period of about 10,000 years the Age of Elvenkind. The empire started as just a small city-state known as Aetheril in the center of what is now known as Aevira's Heart. Eventually as city-state grew, so did its reach. Later, the Aetherii Empire was founded and began to spread its reach across the continent, splitting into provinces. High elves were primarily in rule and inhabited the heart of the empire while non-high elves, dwarves, and other species inhabited the outer provinces.
Centuries later, thousands of humans emerged from the Mist. Caught off guard with the influx of this new species, the Aetherii Empire made a choice, rather than face competition or integrate them into the Empire, they would enslave the species to keep them in line. A few of the provinces disagreed with this choice and welcomed humans in to their borders, leading to the creation of the first Half-Elves. Many Aetherii high-elves saw these unions of elf and human as abominations, sparking many disagreements within the Empire. The Empire then began to invade its disobedient provinces in an attempt to enslave or kill all humans. These provinces that consisted of elves, dwarves, and humans rebelled against the Empire, sparking a civil war that lasted for 25 years.
The Aetherii Civil War lasted two and a half decades, but the Desolate Cascade marked its end, devastating the lands and driving elves to the brink of extinction. With the Empire thrown in to further disarray, human slaves took the opportunity to flee and form their own settlements.