Marcher-Aversarian Wars (concept)
The Marcher-Aversarians Wars were a series of conflicts between the Marchers of Chevalie and the Aversarians roughly between 344 IS to 631 IS, though skirmishes and border wars have been common before and after.
The Wars began in earnest in 344 IS with the invasion of Black Emperor Yakub 'Illspeaker' Yakovad into Chevalie, which brought most Chevalien forces in the Marcher colonies in what is now Kalathipsomi back to the homelands to resist the invasion. Rebuffed from Aironoi by the Astliks and recovering from the Last Dragon Rebellion, the Aversarians invaded the Marcher colonies in their ever-growing desire to dominate more lands.
The initial war was hard fought, with Yakub 'Illspeaker' eventually defeated, Marcher Anti-Magi wreaked havoc upon the Aversarians using guerilla tactics against the rugged outlands of Kalathipsomi. The initial series of wars only ended in 569 IS, when both sides, thoroughly exhausted and struggling to resist outside threats while dealing with the other agreeing to draw a new border. Aversaria would gain the majority of Kalathipsomi with the Chevaliens retaining the Black Mountains and all lands west of them.
Several smaller wars would be fought for the mountains themselves until 631 IS when the Bloodblight wiped out much of Chevalie's nobility and the Marchers withdrew west, Aversarian settlers soon filling their former holdings. The modern border between de-jure Chevalie and Aversaria has remained since.