How about a huge mission that starts in the beginning of a new game, where you find out there is a merciless band of warlords/bandits that are holding the town under their control.
They'd be a full community of up to 9 members.
They have several enclaves under their control, so fewer to help you (to start).
They own the largest base on the map.
Their base is fully upgraded, i.e. all their facilities are installed and working.
They could send bandits to attack you and your allies.