Izzil is the western fort on the central island, in the Southern Badlands. It's populated entirely by Demons, typically called the Izzil Demons.
Originally, both of the Demon factions were under one flag, and both were stationed in Izzil. However, after the Demons took Aieuda from the Elves, conflict arose in their ranks, eventually splitting them into those who wished to destroy old tech and artifacts, and those who wished to keep it. The Izzil were those that wished to destroy it, so the newly formed Aieuda Demons occupied the fort, and prevented the Izzil from razing it.
Fort Izzil is built around a central spire, with a skull face carved into the top.
Just looking at the stats, the Izzil could easily overpower the Aieuda. However, doing so would incur such great losses, that they would be unable to defend either location for any length of time, and therefore neither have acted on their wills.