Essentially, when simultaneous experiments in dimensional travel occurred in Germany and China, a rip in the fabric of the universe was created, allowing Dragons to flee their collapsing world and conquer our own. Soon after, these rips in reality released waves of "magic" that fundamentally altered entire regions, re-awakening or creating the Treants, showing the Atlanteans and Shambhalans that the time had come to return, and showing to the forces of Chaos that had destroyed the Dragons' world our own.
Several hundred years later, almost all of the world's governments have fallen. There are a few small successor states, and in North America the remnant of the United States still holds considerable territory, but the primary powers are the great Dragon Empires. In Europe there lies the Holy Roman Empire, reformed by the Dragons as a reinstatement of feudal government to prevent mortals from growing too powerful. From India to the West Coast of North America there is the Empire of Shenzhou, a dystopian regime that has advanced science to the point of genetically engineering soldiers to fight their battles and police their people.
Between the remnants of the United States and the colonies of the Empire of Shenzhou in California, there lies wide territories of unclaimed land, roamed by pirates from New Orleans wielding salvaged Atlantean technology, a massive city of cars, trucks, and military vehicles, and emissaries from the newly formed Lakes Confederacy. There is the rebuilt Las Vegas, ruled by a rogue Dragon, the small Empire of Deseret, expanding again after recovering from their last attempts at taking land from the Dragons, and the town of Salt End, independent from any of the powers around them, and home to a rare species of mutant.