Well if you think about it Kamion, there really are no rules in war. War is the proof that, on Earth, there are no enforcable rules.

It is only in recent history that anyone gives a hoot about "collateral damage". Take WWII for example. Civilian deaths were more or less ignored. ie Bombing of London, Dresden, Berlin, Pearl Harbour, Darwin, Hiroshima.

Perhaps it could even be said that when civilians know that they will get killed too, along with their armies, they will be less likely to start a war in the first place!