Ryboth has been turned into a shadow of its former self. The Iron Warriors had come and done what they do best. The Death Korps of Krieg had answered the call to save Ryboth, but had fallen into the trap of Perturabo's sons. Legends of siege war; they had prepared for the coming aid from the Imperium and initiated a blockade of the planet. Before even making planet fall, the Death Korps had bore witness to the unrelenting tactics of the Iron Warriors. Besieged from within, and besieged from without; the Iron Warriors held the troop landers at bay as they systematically eradicated the native Ryboth population. They could see the genocide, but they Death Korps could do nothing to prevent it.
With the population out of the way and the primary objective all but lost, the secondary objective was to salvage as much of the forge world's infrastructure as possible. The Iron Warriors would use this to their advantage.
The Death Korps managed, or were allowed rather; to break through the Iron Warriors naval blockade where they found that the infrastructure they were tasked to save was overrun by the bastard traitor sons of Perturabo. Very well then. They would move onto their third objective. The annihilation of the Iron Warriors! A war of attrition would follow as the Iron Warriors closed the gap in the upper atmosphere of Ryboth, trapping the Death Guard in place.
As predicted, the bombardment of Death Korps positions ensued and; as predicted, the Death Korps did what they do best and dug in! But that was some time ago and both sides had been enjoying the conflict to a stalemate. Something had to give. At some point, the lives lost would become finite and there would be a victor. It would be the last man or traitor standing, lest there was intervention!