The Mana Disaster 2000 years ago started because of one Legendary Elven Magician.
This particular Magician had discovered a flaw in the natural laws of Firuman and decided to test this particular flaw. In the end, he had started the Mana Disaster.
That year, the density of Mana in the world was reduced by 90 percent. The whole of Firuman became like a deflated balloon.
That year, the elves were still the lords of the realm. Their might was based on magic, and they relied on magic to dominate the continent. Humans and Beastmen used to be slaves to the elves while the Yabbas, dwarves, and other ancient races were suppressed by the elves.
The result of the Mana Disaster was that the elves rapidly lost all their power. Thereafter, humans, Beastmen, and the other subjugated tribes escaped the power of the elves while the Yabbas and dwarves began to set up their own kingdom.
In the midst of the chaos, the elves split themselves into two factions. One faction retreated into the Dark Realms, beginning to worship the Spider Queen Lolth and using the Dark Arts to change their body and adapt to the darkness. These became the Dark Elves.
The other faction retreated to the Isle of Dawn. This faction continued to teach the teachings of the ancient elves. In order to differentiate themselves from the Dark Elves, they called themselves the High Elves.
This was the history of Firuma
Firuman was a lot bigger than it was now. At that time, there was a strong and knowledgeable race, known as the Aragu. They occupied Firuman's most beautiful landmass, creating an incomparably strong magic empire, producing many illustrious, famous magical works.
However, amongst these magical works, there was one incident that happened. In the midst of that incident, the magic went out of control, and the resulting explosion caused the Firuman continent to break apart into many smaller pieces.
After the incident, Firuman was split into many pieces. The current Firuman continent consisted of the largest piece. The Isle of Dawn was another small piece of land that broke off. According to legend, there was another large piece that drifted off towards the east. Because of the treacherous sea waves and wind, all adventurers that had gone out in search of this continent had lost their lives. In the end, none had brought back concrete evidence of another land.
No matter what, after that incident, the Aragu people and their empire disappeared. The only traces they left behind were stories in the history of some of the tribes in the current Firuman continent.