One side attempts to kill (almost) everyone on the opposite one based on their background. Most of these can be described as genocide, or sometimes even omnicide in more speculative works
Motivations vary, but they most commonly tend to be employed by either xenophobic racists, fantastic
or otherwise, or by the heroes against groups of beings who are (perceived to be) all pure evil
. The former will often signify a crossing of the Moral Event Horizon
, the latter makes the protagonists morally grey Pragmatic Heroes
depending on how the work handles the implications of such an extreme action.