The blood whip was a type of hemorrhagic fever which afflicted the Three Brother Nations 1300 years ago. The name is derived from the whip-like marks left on the walls from victims coughing up blood in their death-throes. Vistria and Verandi were completely devastated by the disease, until eventually they realised that by using divination magic to find those who were infected, they would be able to isolate and cure the afflicted with cure disease spells. Korstraad was less affected as the King employed brutal tactics to suppress the disease.
However, the fear and panic caused by the epidemic allowed a cult of Vecna to convince people to rise up against the governments and seize control of libraries, which they then destroyed. Even the great library of Forge was taken, although the Seneschall was able to drive the cultists off before they managed to destroy the last of the books.