Invasion of Mercatorius

The invasion of the Mercatorius System occurred in 115.M42, with competing factions vying for control of the unstable system.

The invasion came in the wake of the Gracchian Uprising of 114.M42, in which a local warlord of Varachia named Gaio Graccho rose up against Imperial role with his chaotically inclined legion of gangers. Seizing on this instability, genestealer cults which had formed throughout the system chose this opportunity to rise up and seek control of the system.

The year of 115.M42 saw several simultaneous invasions. First of these was a warhost constructed of the forces of Chaos, including the Iron Warriors, Night Lords, and Chaos Undivided who sought to lend support to the Gracchian revolutionaries. Alongside them descended a warhost of Orks, intent in showing their ability to outdo the Ork invasion that took part in the Primus Ruining.

Initial Uprising
The Mercatorius System was considered to be satisfactorily defended, as the system itself was home to the Silver Legion of Mercatorius at a strength of around 1 million guardsmen alongside around a million armed militiamen, planetary defence forces, and arbites. Yet, the guerilla tactics of the Gracchian Legions in the ruined city of Varachia put the Silver Legion and its allies at a disadvantage, particularly as the gangers had a superior understanding of the city's ruins. This led to numerous ambushes and defeats, acting only to strenghten the numbers and resources at the hands of the Gracchian Legions.

Graccho then found himself with the support of the Iron Warriors Doom Company, providing expertise and firepower in the besieging of forts on Mercatorus Prime. The wider legions of Chaos which attacked simultaneously assaulted Novus Mercatorius to stretch the strained imperial forces further. This stretched the Silver Legion even further than previous, with the vast majority of the legion losing their lives over the course of the war.

Invasion of Xenos Forces
The strain put on the Silver Legion increased with the outbreak of Genestealer Cult uprisings and an invasion from an Ork warband. The war turned increasingly to one of survival, as the Silver Legion found itself increasingly unable to hold ground due to heavy losses.

Recognising that the Silver Legion was unlikely to survive the onslaught, Commander Argus requested help from the wider Imperium, which arrived at the turn of 116.M42 heralding the beginning of the Mercatorius Crusade.