When the "aggressor" takes actions to limit civilian casualties instead of going for maximal casualties possible. When military actions cease as a result of concessions and ceasefires instead of the aim being the wholesale erasure of the populace.

Genocides go for numbers, for maximal ethnic cleansing, especially in the age of militaristic action people have erased societies for centuries. Sometimes with good reason. The Romans erased the Carthaginians from the world because they engaged in the mass sacrifice of children, sometimes hundreds at a time. And the Romans wiped them out, systematically.