NPCs do not target the player as if she was the only thing worth killing in the whole world. Your enemies fight against each other when it makes sense to do so.
Alternate name: NPC infighting
The first video game about NPC strife was released on December 10, 1993.
* Peasant mobs attack brigands.
* Rabid animals and carnivorous plants will attack pretty much anything.
* Living beings attack the undead and vice versa.
... and so on.
In strategy games this usually involves hostile "neutral" forces or otherwise more than two factions involved in the conflict with no alliances formed.
Parent groupsImmersion, NPC behaviour
Child groupUnaligned enemies
compare with these groups