It was originally orchestrated by elements of the Night Lords and Alpha Legion in order to provide the forces of Chaos with mercenaries. The sudden rise of the Orks posed a new and unexpected threat to the Imperial defenders.
Currently the Green Kroosade is holding the planets Lethe Eleven and Mordax as well as most of Imbrium and Ulants. Gudrun and Nysa Stromolo are on the brink of anarchy and only the intervention of the Black Templars and Salamanders could prevent the Orks from claiming Thracian Primaris and Enaur Delta. The overall situation in the Scarus Sector is grim and there seems to be no halt to the green tide.