During the Dawn War he worked with Bane; although they hated each other personally they were disciplined enough to work well together. After the war, Bane anticipated the eventual angelic rebellion Asmodeus would launch, and alone of the Gods he was not surprised when it finally happened. Bane wanted to help, but both he and Asmodeus wanted to avoid bringing the other Gods into the fight, and feared that any open collaboration between the two of them would cause exactly that; to avoid notice, instead of soldiers Bane sent aid in the form of advisors and strategy experts. Whether or not this made any difference is unknown, but the devils will deal (slightly) more honestly with followers of Bane than worshippers of other Gods, and Bane's followers are more likely than others to summon and employ devils.