The Invasion of the Daelkyr
The invasion of an alien species to Elvia
In the year 726, a swarm of aberration lead by a mysterious figure only known as "The Corrupter" invaded Elvia. These forces contained Beholders, Mind Flayers, and even some Lycanthropes. Thankfully, the five countries were able to band together and defeat the Daelkyr and even seize some of their technology, using for their own personal means. This is how the technological revolution came to fruition.
It is said that all the Daelkyr were wiped out in the war, but, nobody knows for sure. There are no records of anyone say that they were the ones who killed The Corrupter after all.