We're talking about a big group of ~3000 (possibly more) survivors around 5 years after the downfall. 1% of humanity is still alive, 59% is zombified (classic slow zombies, TWD-like), the remaining 40% of people are dead for good. The zeds recently started evolving into faster and stronger beasts, no one currently knows why. The protagonist gets picked up by a patrol of the aforementioned group. This group lives under a 1984-style dictatorship, but fares quite well overall (and fleeing is not an option for the hero, as surviving on your own became nearly impossible after the zeds slowly started evolving). So the hero has to make the best of it, constantly trying to evade the propaganda that has brainwashed most other members of the group.
The problem is the backstory of the first steps of the establishing of the dictatorship. "5 years after the downfall" is a very short time-span, so we can't go the way of "brainwashing using fear and propaganda over generations". The people remember the time before the downfall, but are disgusted by it and praise their leader. How could this leader have established the basics of the group during the first months of the downfall, and attracted even more members eventhough the totalitarianism is so obvious? I thought about him controlling the only food source in the area, but wouldn't he have been overthrown shortly after people regained their strength after joining?