One of the principles underlying international law applicable in armed conflicts is that no act of war is permitted against the civilian population, consisting, by definition, of persons who take no part in the hostilities.
Until the holocaust of 1939–45, international law gave practically no real protection to the civilian population in the event of war, and was not even intended to do so since up to that time war was considered to be a State activity from which civilians remained aloof. There were, nonetheless, general principles and rules in various international treaties which, in one way or another, related also to the civilian population.