The belligerents are the Frames. As the game starts two Frames are missing. For a very long period of time nobody has received any Testaments from them. The last signal was picked up when both of them prepared for another jump into new unknown world. Later on it turns out that one Frame was destroyed by Filth and the other one has got to a world with slowed-down local time and won't return in the nearest future.
The conflict begins when a revolt starts on one of the first three Frames. People despair of success to find the way out of the Worlds' Chain and decide to set back to Earth. After hundreds years of journey Earth becomes something mythical and legendary for them. The rebels accuse Spirits of all their misfortunes and destroy them. The Frame decides to send out a Testament-Manifesto urging other Frames to end up the meaningless journey and return back to Earth.
Frames followers of the Exodus idea decide to stop the renegades that call themselves the Harkbackhoods. At that moment it turns out that another Frame didn't return from an expedition to a new unknown world. Another Frame from this wave is terrified by this fact, falls under the influence of Manifesto ideas and decides to join the Return (Harkbackhoods).
Frames of Exodus and Harkbackhoods (Return) meet on a couple of worlds and start fighting with each other. Some are trying to go back along the Chain using the Corridors and others are trying to prevent Harkbackhood Frames from doing it. However the Harkbackhoods manage to escape. Psychologically horrified by the battles one of the Frames is almost driven crazy. It declares war on everybody, promises to capture every Frame that gets in its way and substitute the population for "genuine" people.
As a result each Frame becomes drawn into the conflict. Each side in this conflict has its own unique features. Altogether there will be 6 Frames to play for. Three other Frames are out according to the scenario.