The fall of Perosa might be described as Hell breaching the blocked mountain pass, but in truth there were many subtle factors that all came into play to bring about this catastropic event. The ocean of Hell has been eroding the stalward Vandien Spine for centuries to no avail, but subtle manipulation often has a greater effect. This bares true in the case of the assult aginst the Vandien Shield.
Perosa's fall really begings several decads prior to the begining of Hell's initial assult. The seeds of corruption were scattered and made to be carried to the corners of Taigus.