So. Here goes:
The identity (of action, of belief, of feeling, of interests) between a military force and a civilian population is an empirical variable.
A prime requirement of justice in warfare is to target the opposing military force in opposition to the civilian population associated with it.
Justice in war demands that the required identity and non-identity of the civilian population be a real fact.
that is to say
A military force can only make war legitimately if the civilian population in the area it is fighting in is
a) reasonably believed to be in active united majority support of that military force;
b) reasonably believed to be in active united majority opposition to the opposing military force.