The O'Brien Empire is one of the six principal political organizations in the Yulan Continent.
It borders both the Anarchic Lands and the Rohault Empire. The O'Brien Empire was founded by the War God, who possesses the highest level of authority, followed by his personal disciples, and then the emperor.
The O'Brien Empire possesses many Saint rank warriors but Saint rank mages were a rarity.
After the events of book 13, the O'Brien Empire was taken over by Highgod Adkins, who destroyed War God mountain and killed the imperial family at the imperial palace.
After Adkins' death at the hands of Beirut, the O'Brien Empire was restored again.
Curretly O'Briem exist no longer it's former land is ruled by Baruch Empire.