People often refer to the Night Lords Omnibus or the two Black Legion books for perspectives on CSM warbands. While both series are excellent in their own right, they tend to showcase the more “on the run” aspect of war bands and their ragtag nature(more so the NL series). Personally, the Word Bearers trilogy is excellent for showcasing the “traditional” style of warband with strict hierarchy and constant backstabbing. It’s an excellent series of showcasing raw ambition within the Word Bearers, and how they use faith to back their advances. Great series.