Most other creatures believe demons to be little more than mindless engines of destruction and violence. If that supposition were true, the Blood War should have ended long ago, since the tactical and strategic genius of the archdevils would have made quick work of the hordes that erupt from the Abyss. In fact, even though demons are quintessentially chaotic, their evilness combines with that outlook to produce a fiendish, subtle shrewdness. Demon lords and other powerful entities exert control over their armies that enables the forces to accomplish goals that would be beyond the capabilities of a leaderless mob. To the demons that have intelligence enough to appreciate their role in it, the Blood War offers an endless source of diversion underscored by resentment of a cosmic order that refuses to admit their superiority.
As the devils have surmised, the demons invade Avernus because it is easily accessible from the Abyss. But some sages and demonologists maintain that even if that were not the case, the Nine Hells would still be the demons’ prime target. If the demons sent out a large force to invade a different plane, this theory holds, the devils would be able to marshal allies from across all the planes to rise up against the Abyss and end its threat forever. Instead, as long as the demons focus most of their efforts on the doorstep of the Nine Hells, realms such as the Seven Heavens and Bytopia are loath to commit aid to defend a plane that is inimical to everything they stand for by aiding the devils directly.
Therefore, the demons assault the Nine Hells over and over not only because it is the greatest threat to their dominion, but also because striking in force anywhere else would play into the devils’ hands.