The Illyonavich dynasty had ruled for centuries bringing peace and good life for the common folk. They ruled from the royal tower on the island, which is to say Prince Royal Island. With the advent of Prince Mychal Illyonavich as emperor of the world, the world felt a shift. He felt compelled to rule not only the world and it's systems but divinity itself. He became god in his own eyes. This led to chaos and horrific times. He decided to destroy his rebellious world and he brought d-day into the world. He launched himself, his loyalists and many slaves to the safety of his space palace and from there rained down fire the likes of which cannot be described. It flattened the world and every city except one, Oxbridge, the former capital of the world. It stands to this day, still filled with a violent form of radiation deadly to the living. It was this d-day event that brought the undead into existence. They were immediately hunted as if some horrific monstrosity. Wanting only to survive a group became good at running. When they tired of running they stood their ground and dealt with the emperor.
While the emperor was gone his sick and vile religion remained. On Prince Royal Island, in the time it took the new Resurrected nation to build its city the sick religion transformed the descendants of the loyalists into the nation of The Elite. The religion was forcefully rejected by the d-day survivors and the slaves who managed to escape thus forming the nation of The Scarred. With the living hunting down the Resurrected like animals the new nation had no choice but to defend itself. In the end the dead claimed the island. What happened on the main continent, Terra Dominata, during this time is unknown.
Having gained their peace and solitude the dead learned they live in the real world and problems come running to find them. Terra Dominata had grown into a monster ruled by yet another man suffering from a god complex. He looked across the channel and set his eyes on Prince Royal Island. The dead were again forced to act. When the business was done the dead found themselves in a very unfamiliar position. They could remove their enemies, the living, entirely or offer a peace deal. Life and death lay in the hands of the most hated people to ever exist. They offered up the Economic Accord, a deal which included trade and commerce between the two people with the dead in command. The living, not wanting to die, accepted and the war was done.
Now we look back and see the deal must have worked. While the living are not allowed on Prince Royal Island life is working just fine everywhere else. The dead do not attack the living and the living do not attack the dead. Everyone is paying taxes to keep the world afloat and at last, now with the natural death of the last of those living who remembered the conquest there is peace and harmony.