The Pax arose after the long chaos of the Colonial Wars in the Sol System. It was created by those calling themselves the Ratu, sometimes using elections, sometimes using force, always using subtle manipulations amid the chaos. For over 10,000 years, the Pax ruled all of Mankind, shepherding the spread of humanity across the stars throughout the galaxy.
Always at the forefront of the Pax were the Ratu, those humans blessed with psionic potential. Local rule was allowed, but the Pax controlled all interstellar affairs. In its drive to maintain the peace, the Pax pushed its psionic explorers and terraformers further and further out. Each new world would be home to only one or two groups. The goal was the separation of ethnic and nationalist groups for peace. On worlds that could not be easily terraformed, the Pax also adjusted the people.
While they found life, nowhere was life as robust as it was on Earth. World after world followed the examples of Mars, Venus, Luna, and the other great moons of Sol and were transformed into new homes for the children of Earth. Sometimes, the colonists were changed to fit the planet, with the same technology used to make different Children of Earth
Covering the entire galaxy, the Pax took over a year to cross by ship. The use of telepathy was all that kept the far-flung civilization connected.
The Pax collapsed when a psionic plague started in hyperspace. It struck across the Pax, killing or disabling all those with high levels of psionics. Technology that required psionic operators were useless, communications ceased, ships could not move.
With the loss of the binding psionics of the Pax, interstellar civilization collapsed utterly. For 10,000 years, the Children of Earth on various worlds struggled to cope and build new civilizations. With all common technology unusable, most worlds were reduced to pre-technological states.
Organisms with psionicly-altered genetic structures (including people) began to change out of control, responding to the uncontrolled emissions of lesser minds. Worlds that might have maintained interstellar flight found themselves fighting to stabilize their un-tended ecosystems.
Slowly, some worlds fought their way back to civilization, and eventually regained the stars. As they expanded, they found other worlds, in various states of technology, with humans in various forms. The Imperium is one of three large powers within what was once the Damascus Parish of the Pax. Along with the Midakoate and the Paxton Commonwealth, it carries the torch of intersteller civilization.