The Angel War was the crescendo of the escalating conflict between two groups of angels. Basically, one group opted for a “resetting” of world 45 while the other group pointed out that such an act would wipe out all life just because of “petty sins”.
The anti-resetting group found themselves in minority among the angels, and started recruiting other species for the upcoming war. When the demon hunters of world 20 got wind of the events they put aside a few of their troops to support “whichever side who DOESN’T aim to wipe out humans”. They soon noticed that the angels had a little too many advantages, and the flying simply became the last straw. That’s when a memory keeper presented herself and suggested an array of other allies, as well as a way to command demons – the natural enemy of any feathery being.
After the war it was decided that the twelve hired demons would be a fixed part of the armed forces and (after a proposition inspired by Eileen) a habitat was constructed in world 34. Since the demons were such an asset when fighting less cooperative species, a program to recruit so called demon traitors was started. The demons (as well as possible family members) were offered housing in the habitat if they’ll peacefully agree to the contract.