The rebellion of the people of Erna from the Carthic Empire, 300 years ago, was a foundational moment in the history of the modern nations. A combination of natural disasters, corruption and stagnation, and weak emperors loosened the grip of the empire on its sister continent. The rebellion utterly destroyed the empire's influence on Erna, and eventually dissolved the empire itself. Each region threw off the yoke of their oppressors in different ways, and the aftermath of the empire's defeat and withdrawal set the political stage for centuries afterward.
The Carthins had their own calendar, which was largely rejected when their empire lost its hold on Erna. A new calendar of years gained prominence that started with the Harkath Rebellion, with CA (Cartha Ascendant) tracking backward and AE (After Empire) tracking forward. The Rebellion began in 0AE.
The rebellion began in the northeastern regions of Erna which now make up the Kingdom of Harkath, the lands farthest from the empire where its control was the most difficult to maintain. Hale Harkonnen, a wealthy noble who chafed under foreign control, rallied the rugged people of the area into an army which quickly and easily destroyed the local Cartha governor and his establishment. Spurred on by this victory, thousands more flocked to Hale's banner, and the Harkonnen war machine marched southward with the idealistic goal of driving Cartha from all of Erna.
The Empire's Counterattack
However, the Harkonnen campaign's progress soon came to a crashing halt. The farther the people of Harkath marched from their homes, the weaker their conviction became. Eventually, Cartha rallied its reinforcements and launched its counterattack, which met Hale's armies south of the Tarmane Sea, in the middle of the continent. The fighting was constant and fierce, and neither side made any significant gains for almost a year. Eventually, Hale withdrew and consolidated his forces along the coast. In 3AE, the forces of Jetstone marched out and joined the fight.
Fortunes were swinging in the favor of Harkath and Jetstone when the Fallen Kingdoms of the west proclaimed their independence from the Empire. This put the Cartha supply lines in enemy territory, and to avoid having their armies completely cut off, far from home, the Empire capitulated and recognized the Fallen Kingdoms' independence immediately. This proved to be a final, crushing blow to Cartha moral, and in 6AE its armies pulled all the way back to their homeland. This war proved to be the main military engagement of the rebellion.
The Fallen Kingdoms
The scattered kingdoms of western Erna were the first to fall to the Cartha's initial advance centuries earlier. The kings, queens, and their families fled as their armies were defeated and lived in exile for generations, nurturing their grudges. When Hale Harkonnen succeeded in driving the Empire from his lands, the kings took this as the perfect opportunity to reclaim their birthright. They rallied whatever forces they could under ancestral banners that hadn't been raised in generations, and marched on the Carthin government buildings. Though the force the royal families had raised was disorganized and largely untrained, the local governors had sent most of their standing forces to the eastern front. Faced with the prospect of protracted fighting down the fallen kings to secure their supply lines to the real war, Cartha quickly realized their independence and signed a treaty of nonaggression.
Despite the fact that the efforts of the Harkathans had allowed the Fallen Kingdoms to rise to power with almost no difficulty, the new kings signed pacts with the Empire to protect themselves and sent no troops to the front. Hale Harkonnen viewed this as a direct betrayal of the People of Erna's common goal, and seeds of enmity were sown between the two nations which persist to this day.
Ecaz and the Puppet Government
While many communities suffered under the yoke of the Carthic Empire, the people of Ecaz found a way to peacefully coexist and even prosper with their masters. Several successively weaker leaders allowed the people of the four districts to insinuate their way into the governor's organization. By the time of the Harkath Rebellion, most of Ecaz was self governing, with the Carthin governor living a luxurious life in a palace built for him, well out of the way. The Ecazi were unwilling to let Hale's war endanger their comfortable circumstances, and they took up arms in defense of the empire. However, the experience and resolve of Hale's forces far outmatched the Ecazi defense forces, and they were thoroughly routed in 6AE. Ecaz lost control of its northern two districts permanently and earned the hostility of its neighbors for centuries afterward.
The Dwarven kingdom of Jetstone was one of the oldest powers on Erna at the time of the Carthic Empire's advance, and while their forces were defeated on the field of battle, they endured and maintained their national identity under Carthic rule. This was made easier by the fact that the largest Jetstone cities were underground, and few Carthic governors enjoyed the claustrophobia of administering such places. As long as the dwarves continued to pay their taxes and their tributes, they were largely left alone. This allowed the long-lived and patient dwarves to gather their forces and bide their time, waiting for the time to strike. That time came when Harkath rebelled. After waiting to see how successful he would be, the armies of Jetstone poured out of their mountain fortresses and clashed alongside Hale with the Carthic counterattack in 4AE.
The empire put up a valiant struggle and the fighting stretched out longer and longer, but the dwarves of Jetstone held their front, and with the rebellion of the Fallen Kingdoms, the empire withdrew completely. During the fighting, Jetstone ended up expanding their borders significantly from before Cartha took over, and since many dwarven memories were long enough to remember a time before Carthic supremacy, Jetstone didn't view the empire's reign with as much hostility as the human nations. In fact, the King of Jetstone signed a truce with Cartha once their forces arrived home, and that treaty (combined with the logistical difficulty of marching an army across the world and a narrow sea) ended Harkathan hostilities against the empire.
The Other Nations
The lands that make up Ruud today were just as rugged during the times of the empire's reign as they are today, and few Carthic settlements were made there. As a result, the local populace knew little Carthic control and didn't participate at all in the rebellion.
Tandrice was almost as far from Cartha as Harkath was, and the Empire's control there was similarly light. Tandrice didn't fight for their freedom until Jetstone officially joined the fight, which almost completely cut off the local Carthic forces and made their fight for freedom trivial. The seeds of Tandrice's civil war were already growing, and the nation sent no troops to fight in the larger conflict against the empire.
Willesa, whose cities had already gained a reputation as centers of art and culture (not war) put up little to no struggle against Carthic rule. When the empire's hold on the continent broke up in 6AE, it pulled out of Willesa, leaving it largely undefended and to its own devices.
Historians know very little of the history of Jakka during the time of the empire's reign, and it is believed the empire had little to no presence on the island, due to the volatility of the Sea of Storms. Jakka didn't have any major interaction with mainland Erna until after the rebellion had concluded.