Revolution
This was when Dregia rose up against the overstretched Augustian army and became an empire of its own.
The Augustian military was stretched thin by a war in the Far East, with a nation called the Yogisu, beyond modern Dregia. They were losing, and near full retreat, the slaves of the Empire saw an opportunity. They revolted, killing their overseers and owners and dug in, cutting off the army from the homeland and trapping them between a new nation of angry revolutionaries and a foreign nation they were unsuccessfully invading on the verge of routing them. His army weakened and at the mercy of the former slaves, the Augustian High Priest (in the absence of the dead King Aupuntis) recognized them as an independent nation, and entered a peace treaty with them. The new Dregian Empire (Dregia is an old Augustian word synonymous with Freedom) allowed passage of his remaining military back home and the Augustians made peace with the Yogisu.