The War of Deucalian Secession , also known as the "Halcyon Civil War", began during the early stages of the newly formed Halcyon Empire, with the king of the Deucalians, Gilgamesh, formally seceding from the Empire, strongly believing that Imperial rule and authority threatened the autonomy of his people.
With the creation of the Empire, and the incorporation of all four nations as Imperial provinces, with Zymith being the capital and Aulus Megellus as the newly crowned emperor, there was much skepticism and scrutiny from some of the populace. Many felt that under Imperial administration they were no longer truly independent, having to be obliged to an emperor whom they saw had no relevance nor importance to their own interests. The most prominent group of people who shared this perception were the Deucalians and their king, who above all others, felt that their independence was being threatened by being a part of the Empire.Seeing no reason to delay further affiliation with the Empire, Gilgamesh formally declared that his nation and people would have no more correlation to Imperial affairs or sovereignty during a meeting in the presence of the emperor. Insulted at this sudden act of treason in the eyes of those loyal to the Empire, Gilgamesh was driven out of the city of Zymith and labeled a traitor and a coward. An immediate call to arms was called through the provinces, as the Imperial army was mustered inside Zymith in preparation for war. Once all forces were gathered, a small vanguard of cavalry led by Emperor Aulus Megellus himself rode to the stronghold of Deucalia to deliver the declaration of war to King Gilgamesh in person. After war was officially declared, the Imperial army immediately began to march out of the gates of Zymith towards the bridge that connected