This is a small piece I have written as a preface for the Player's booklet of a Birthright campaign I'm planning. The campaign will probably remain at the adventure level, though. This pretty much intended to set the tone. Sorry for the length.

"Fall of the Justminian Empire and the Battle of Deismaar
Although the Justminian Empire had not considered action when the people of Masetopolis (and the entire province of Masetium) began a series of migratory movements from the satrapy of Lucitia to the northern continent of Cerilia, this movement encouraged three groups of peoples to follow suit, the Rjuven, the Brecht and the Andu, who took great advantage of their distance to the Justminian capital to retain a great autonomy. They were preceded in their movement towards Cerilia by the Vos and the Basarji, but as they fell outside of Justminian sovereignty at the time, they were largely ignored by Imperial Chronicles until geographers began to explore the northern continent.
Successive emperors attempted to slow this movement, by relaxing the tributes, granting citizenship, offering to build up their infrastructures, even by granting increased freedom of religion, but these improvements of their conditions were short-lived as each threatened the power of the empire.
The harsh emperor Azraikurr (son of Azrai) took it upon himself to restore Justminian sovereignty over the northern tribes. Although we can establish that he was the one to turn the Justminian civic cults into mandatory monotheistic worship of the god Azrai, the Justminian Chronicles tend to be confuse, even sometimes contradictory, on this character. In many ways, this can be expected for the Emperor who, in history's view, killed the empire.
What the chronicles do tell is that he allied with many peoples and made many contradicting promises over Cerilia, giving sufficiently vague promises over Cerilia to his mercenary commanders to create a power void by way of internal conflicts without having to fear the possibility that his former allies would ally against him.
All considered, the tactic did leave a great risk, as many of his new "allies" were uneasy working together. This complete lack of cohesion among mercenaries could have cost him the war, had it been a traditional engagement.

As things stood, the nations of Cerilia had reasonably well consolidated positions on the new continent, and negotiated a defensive alliance between the Justminian exiles and the Basarji. Many scholars have speculated that the reason why the Vos were left out at first was due to the constant border skirmishes between the Vos and their neighbours. Still, a few Vos managed to establish a working peace with their neighbours.

The date of the battle of Deismaar is uncertain, but if the datation is correct, it happened on the 1st year of the current era. Probably on the month of Deismir. The battle is of little interest to students of the military arts. By the time the Justminian army arrived, the mercenaries were nearly turning on each other, and a few of them quickly changed sides. One of those who stayed was the prince Raesene, who now took the surname Andu. A bastard child of the predecessor of Roele as king of the Aenwe, he revendicated not only the Aenwe crown by virtue of being the eldest child, but the entire Andu lands.
The battle was a short affair, as not long after the initial clash of the armies, what was certainly the most powerful volcanic eruption to this day destroyed most of the pass, killing many leaders and thousands of troops on both sides. Among them Azraikurr and Roele's brother Haelyn. The death of Azraikurr provoked the disintegration of the Justminian army as its mercenaries' renewed hostilities slowed down the retreat. By the time both armies had left the area affected by the lava flow, there was too little left of the Justminian army to stop its provinces from declaring independence, and this power void resulted in the current make-up of the Adurian continent.

On the Cerilian side, this battle left the Masetians weak as a tidal wave caused by the eruption destroyed the vast majority of their navy, and the power void also affected their side has the formerly allied armies quickly renewed their former hostilities. For Roele, now king of the Aenwe, the battle provided he greatest surge in ambitions. Obscure scribes had already started writing of the event as something that had been powerful enough to destroy the gods, and others followed this idea. Roele quickly proclaimed that his brother Haelyn, who had been a priest of Anduiras prior to his death, had now ascended to replace Anduiras, and that he was himself imbued with the blood of his god. Ambitious leaders of other nations imitated Roele, but had more limited success. The consequences of these beliefs will be discussed in greater detail in the Tomes on Cerilian history.

Universal History of Aebrynnys, Tome 2 (Aduria: the Justminian Empire).
Collection Published by Anuviere & Bauer."

The text makes a few assumptions for the purpose of filling in a few blanks, or solving things that I personnally considered problematic. I use the unofficial Aebrynnys map, although I'm still juggling with the size. It also makes a few assumptions that will probably turn out to be false because of their intent to rationalize events which happened over a thousand years ago. The chronicler makes a few assumptions about bloodlines which could be thought as cavalier from a meta-gaming point of view, but for comparison, I'll just mention that the king of France was said to have thaumaturgical powers (including the healing of "écrouelles", a lesion provoked by a disease of the same family as tuberculosis, which he did by laying on hands on the day of his official coronation). I used someone's material on the 12 duchies for the 5-6 Andu tribes, but consider them as future separate nations (by language at least). I also roughly divided the other Cerilian groups in future nations.

For the years, I'm still internally debating whether I will use the HC years as equivalence or put them a century later (thus the 17th century for Cerilia would be the 16th for us).

Alignment has no tangible effect and little influence on my game. The spellcasting clergy will remain, but the metaphysical implications on the nature of divinity will remain somewhat obscure. The discourse on Haelyn is an effect of the Cerilian renaissance, and local or lesser divinities form a part of the continent's pantheons; some of the younger divinities are just rehashes of older divinities. Azrai becomes a more ambivalent Saturn/Chronos figure (although they were identified as the same god, Saturn was a much more benevolent figure than his hellenic parralel), with a tendency to accentuate his Chronos side due to his identification with the Justminian empire's later years.