Cabal is a series of maps by Sverre André Kvernmo (Cranium). They were to eventually become a 32-map megawad, but when he was contracted to contribute to the Master Levels for Doom II, he sent the twelve maps he had already finished for this project. Five were kept, and the other seven were later released as the Cabal series.
The protagonist in the Cabal series' story is not the usual space marine, but a cyberdemon lord betrayed by his peers and transformed into a human. Driven by the desire for revenge, he sets out to slaughter the conspirators and all those who now serve them instead of him.
The level progression would probably have been something relatively similar to this:
For instance, Derelict Station's story explicitly mentions being found after escaping the Sea of Blood; the "Express Elevator" is when the Cabal starts to notice the player is still a threat to them and logically comes just before "We who are About to Die" which is when they start fighting back; and the "Black Tower" is said to be near the end of the player's journey; while "The Image of Evil" was meant to be the "final showdown".
- caball ("all the cabals", basically) at Doomshack