This month’s Apocrypha Necromunda is set in the city’s distant past, in the Age of the Gang Kings. Necromunda was new to the God-Emperor’s fold, so at that time it was still a bit more of a wild west. Entire Hives were at war against each other.
Hive of Blood includes a scenario called War in the Wastes, as well as rules for mass battles in the Age of the Gang Kings.
You can download Hive of Blood here.