In the year 2038, humanity ascended to the heavens in a way that no one ever expected. Two races from distant stars, united by an immortal Empress, offered mankind a place in their interstellar community. When met with a mixed response, the aliens quickly forced the defiant ones to comply. Concerned with Earth's ecosystem, Empress Materia shipped billions of humans to other planets. Many of these planets being freshly terraformed frontier worlds. Mars and the moon were eventually converted into massive cityscapes. Many humans, as well as members of the two alien races, felt that the Empress Materia's actions were authoritarian and unnecessary.
Over the next five and a half years, a grassroots movement to succeed from the empire grew rapidly across predominantly human worlds. Eventually, certain members of the movement concluded that violent revolution was the only way to achieve their freedom. On March 6th, 2043, a coordinated attack on the empire's capital took place. The planet erupted into chaos as the rebels desperately fought to reach Materia and kill her. Despite the rebel's best efforts, imperial forces swiftly crushed them. Although they failed their goal of overthrowing Materia, the insurrectionists made a lasting impact on the empire for centuries to come. By 2065, the streets of almost every predominantly human world were filled with secessionist protesters. Cities suffered from numerous riots. The secessionist movement had reached critical mass, and everyone knew it.
Then, Empress Materia announced something truly unexpected. Any planetary population who desired independence from the empire could succeed at any time. Over 60 star systems immediately succeeded from the empire in the following years. While free to govern themselves, the empire would no longer be supporting them in any way. The greatest effect of this was the massive regression in technology. Free systems were forced to mostly use older tech, due to the astronomical energy costs of imperial designs. This caused interstellar travel to become slower and more expensive.
The year is currently 2344, the independent systems are more isolated from the empire than ever before. Never have they been so divided. Rotting nations battle over control of resources and territory. Single planet states struggle to keep their trade routes active. Pirates plunder poorly defended settlements on the frontier. Wherever you go in the Outer Worlds, there's no peace that truly lasts.