In the year 3550 AD, the Terran Empire had expanded to well over two hundred star systems, encountering thousands of planets and dozens of races. To the human-supremacist Empire, these races were little more than insects to be eradicated.
This led to dissention among the people of the Empire. Many felt that these aliens could bring wondrous new technology and culture to humanity. Others felt that the autocratic government structure of the Empire was oppressive, and rebellion slowly began to spread throughout the colonies.
In 3575, Devan Carter, a diplomat, rose to power as the governor for Madrigal III, a planet known for its sprawling supercities, abundant resources and immense shipyards. Carter loathed the Empire with all his heart, so he used his newfound power to sow the seeds of rebellion among the governors of the Madrigal system, which contained over a dozen planets.
Using his incredible persuasive skills, Carter launched a full-blown propaganda campaign on Madrigal III, designed to paint the Emperor as a xenophobic tyrant. Using ancient records from well over a thousand years earlier, he showed what kinds of horrors were born from xenophobia.
The campaing proved successful on Madrigal III and even spread to some of the other planets in the system. Soon, anti-Empire speeches were being used by politicians in their campaigns.
By 3625, the system had all but seceeded from the Empire. It refused to answer long-distance communications from Empire-occupated systems and even allied itself with the Sophons, blatantly disregarding the Empire's "no-aliens" diplomacy. Even after Carter's death in 3630, the Madrigal system was the hub for all Rebels fleeing their homeworlds.
The Emperor, furious at the loss of the entire Madrigal system and afraid of losing more, declared outright that any citizen who speaks out against The Empire would be immediately put to death. This led to many thousands of people fleeing their homeworlds to find a place with the Republic. However, the Empire foresaw this and had placed a blockade around the star lanes connecting Madrigal to Empire-controlled systems. Many people lost their lives trying to flee the tyrannical Emperor.
The period of time that came to be known as The Secession officially ended in 3690, with the Empire consolodating its forces to prepare for a major offensive.