Quote Originally Posted by Proud Tortoise View Post
Why would it need outside intervention to keep it going?
In order to prevent either side from actually winning it or even just gaining too great an advantage, naturally. The Blood War draws off some of the energy and power of two really nasty places and pits it against each other, and a significant number of parties on the other Planes think that is preferable to having that energy devoted to messing with their own Planes instead. So they intervene to make sure the Blood War stays in its eternal stalemate.