Aregrionno's history knows several distinct periods.
Settlement
Going as far back as the First Era, the Aregrionnic peninsula was said to be the Garden of the Elves, a land of mountains, hills, wine, and fruit. Men and other races arrived during the Second Era, and settled around the region.
Elven Occupation
Elven legend tells of the harmonious co-existence of Man and Elf; myths told by Man tell of Elven oppression, and how Man was enslaved to work the land. The degree to which these stories are true (and not just propaganda made up in later times to incite Elven hatred) is unknown.
Elves were a prominent presence in the peninsula up until the kerymsept. The degree to which the kerymsept was an effect or a cause of changes in the region is unknown. What is known, is that a rebellion took place (called the Rivolta in folklore).
Imperial Age
Whether the Elves were violently overthrown or simply left to focus their attention elsewhere, the result of the Elves leaving the peninsula was that a new power took its place: the Aregic Empire. Led by a royal bloodline that is only known as Aregion, this empire soon found itself in control of the territories that make up Aregrionno to this day.
The largest city of the land was renamed Unknown, and the various vals were instituted to rule the land effectively.
The exact length of their rule is unknown. It was started near the beginning of the Fourth Era and did not exist during The Year of the Black Star. Most scholars do assume this empire lasted for nearly (if not more than) a thousand years, however. All this time, this empire was led by an emperor simply known as Aregion, but this being a single individual for all this time seems unlikely.
Guild Age
The division of Aregrionno into various guilds made it manageable to rule, but also proved to be the ultimate downfall of the Empire itself, as it allowed the various regions to unite against the ruling body more effectively. In a long conflict known as the Guild War, the various orders of labor united and overthrew their emperor in the late stages of the Fourth Era.
This led to the various guilds finally uniting as a ruling body to govern the land instead of the crown, and The Covenant of the Three.