Ok I say that if the dev can create like a Alfa Zombie that can control the one horde if you kill him that is very hard because the zombies can defend him. If you kill the Alfa zombie the horde will scatter and then if the zeds found another zombie Alfa they can form another horde or the zombies that no have one can create 1 horde whithout a alfa zombie (vanilla hordes) .Sometimes hordes can have like 2 alfa zombies depend the size , the zeds will follow the alfa zombies until he decease. Alfa zombies will spawn sometimes spawn but they can help to the difficult in the game , so zombies can for they own hordes in the first days and then alfa zombies start to appear (you can put in the option menu if you want them or change the probability to spawn)