Archived: Great Sundering

The Great Sundering, also known as the Molosian Heresy, was a galaxy-spanning civil war that consumed the worlds of Mankind for 9 Terran years. Its outbreak marked the end of the Emperor of Mankind's Great Crusade to reunite the scattered colony worlds of humanity under a single government and the beginning of the current Interregnum. The Great Sundering is in many ways the founding event of the Imperiums of Man as it now exists.

The seeds of the civil war began following the internment of the Emperor of Mankind in the Golden Throne after sustaining life-threatening injuries after a series of events. His failure to name a Warmaster to lead the Great Crusade led to a split between those who supported Uriel, the 'firstborn' and favoured by the Terran High Lords, and Cleophus who also commanded great respect amongst his brother Primarchs and the Imperium as a whole.

Cleophus convinced near half of the other Primarchs and Space Marine Legions, as well as large swathes of the Imperial Army and the forces of the ancient Mechanicum, to support him against Uriel, who he believed who destroy the Imperium and all it stood for.

Unbeknownst to Uriel and Cleophus, the Ruinous Powers had been steering the conflict from the shadows and used their agent, First Captain of the Knights Azure, Molosan Trein, to influence events to their advantage. Molos and his followers spread the seeds of Chaos throughout the Legions and would finally reveal their treachery at the Batle of Valinkesh in the later years of the war.

Molos' gambit would ultimately fail, despite crippling many Legions at Valinkesh, during the Siege of Terra, and he and most of the other Traitor Legions were hunted as they retreated to the Eye of Terror. The fragile alliance that had formed to combat what was deemed the greater threat did not hold, with Cleophus and his forces securing half of the Imperium but forced to retreat from Terra after a short skirmish.