|Attacker||Halo Brethren, Imperial Fists and Sable Swords Chapters|
|Defender||Eversor Temple (Officio Assassinorum)|
In 546.M32 the byzantine politics of the Imperium of Man took a calamitous turn when the High Lords of Terra were all assassinated by the orders of Drakan Vangorich, the Grand Master of the Officio Assassinorum. A Space Marine retribution force was drawn from the Halo Brethren, Imperial Fists and Sable Swords Chapters to track the Grand Master to an Assassinorum temple. The Astartes commander of the strike force was assassinated as soon as he made planetfall, but his fellow Space Marines commenced their attack nevertheless. Within the temple, they were assailed by 100 Eversor Assassins. A single Space Marine survived the onslaught to reach the Grand Master and deliver the Emperor's judgement with his Bolter. The Imperium swiftly descended into anarchy as rival factions fought for supremacy and the open seats on the Senatorum Imperialis.
This sorry situation would last for almost a full standard century, until Chapter Master Agnathio of the Ultramarines gathered the support of over 50 of his fellow Chapter Masters from all over the galaxy, and a combined armada of over 50 Chapters of Space Marines descended upon Terra for the first time since the end of the Horus Heresy. Agnathio provided the warring factions with an ultimatum to either cease fighting and form a government immediately or be purged as Heretics. The factions, unable to withstand the military might of the equivalent of an entire Space Marine Legion of old, quickly fell into line, and a new set of High Lords of Terra were quickly elected and order restored at the heart of the Imperium.
- Warhammer 40,000 Rulebook (6th Edition), pg. 169
- Warhammer 40,000 Rulebook (5th Edition), pg. 124