Raxos Civil War
Civil war came to Raxos when the Planetary Governor managed to have a portion of the world's Planetary Defense Forces launch an uprising against the planet's own regime. The coup initially was largely bloodless, but everything changed when the insurrectionists seized a Deathstrike missile battery and unleashed a massive bombardment on Raxos, which disrupted its very tectonic stability. Millions died in the span of a few days and the Governor was revealed to be the Changeling, a Daemon of Tzeentch. Harnessing the psychic upheaval on Raxos from the mayhem, the Changeling opened a portal and summons hundreds of fellow Daemons.
Alerted to the situation on Raxos by Inquisitor Karamazov, four Brotherhoods of Grey Knights led by Grand Master Drystann Cromm arrived on Raxos amidst the slaughter of the populace. By this point a handful of the planet's PDF was left to desperately resist the Daemonic legions of Tzeentch. Dividing his forces into four strike forces, Cromm sent three to close the Warp portal and the fourth, under Brother-Captain Stern, to reinforce the planet's spaceport defenses. Falsely secure in their earlier victories, the Daemons were taken by complete surprise by the Grey Knights. Cromm slaughtered all in his path and sealed the Daemonic portal with the broken fingerbones of martyred Saints, in conjunction with the ritual of cleansing and exorcism. Meanwhile, Stern had overseen the evacuation of the planet's remaining refugees by interplanetary shuttle.
Stern, by this point, grew uneasy when he discovered that the Changeling was still unaccounted for. Realizing that the Daemon must have hidden on one of the refugee shuttles, Stern reluctantly ordered his Battle Barge to open fire on the shuttles. Hundreds of thousands of innocents were slain in the ensuing salvo.