Secessionist Union

The Secessionist Union was a former league of rebellious worlds and organizations that was active during the earliest years of the Insurrection, until its dissolution in 2504. Formed in 2487 to protest against the worsening conditions in the colonies, it eventually transformed into a military-minded organization that advocated for direct conflict with the UNSC. It was eventually succeeded by the United Liberation Front.

History
Growing rapidly thanks to the outrage caused by the UNSC's nuking of Far Isle, the Secessionist Union was further strengthened by the influx of material, vehicles, and recruits from sympathetic elements in the Colonial Military Administration. They launched a series of well-coordinated attacks following the Callisto Incident in 2494, outright capturing a number of colonies such as Eridanus II and Levosia, with their concentrated armies and fleets of ship allowing them to enforce their control over these territories. That said, as the Union forces only struck government and military targets, and the planets they captured already had vocal supporters for colonial independence, they enjoyed huge public support in these areas.

The success of the Secessionist Union, however, would ultimately work against it. The UNSC swiftly deployed overwhelming numbers of modern ships with detachments of UNSC Marines in large counter-insurgency campaigns, often beating back rebel forces with minimal casualties. Though hampered by traitors within its ranks, the CMA collaborated with the UNSC to reactivate Project ORION, humanity's first modern supersoldier program. However, the discovery of a list of known sympathizers within the CMA forced the organization to cease supplying the Secessionist Union, forcing it to rely more and more on terror attacks and guerrilla methods after 2496. The assassination of its leader, Jerald Ander, during Operation: KALEIDOSCOPE quickly led to its dissolution and splintering in 2502. Though it was eventually revived under Nanci Ander, it would never again regain its former strength.

The Secessionist Union marked an important realization for independence movements. While a centralized structure allowed it to fight toe-to-toe with UNSC forces early on, it left it vulnerable to the sabotage of key equipment and the assassination of important individuals. Though the UNSC hoped that its collapse would deter future rebellions, it instead seeded battle-hardened freedom fighters throughout the Outer Colonies, who then used their own experiences to create hundreds of cells. Each of these fought with their own different doctrines, tactics, and attacked different targets, making it far harder for the UNSC to counter the spread of the civil war.