  Once the fighting begins two central principles guide evaluation of whether the war is being conducted fairly: one which respects the distinction between combatants and noncombatants (The Principle of Non-Combatant Immunity) and another that governs what counts as the proportional use of force (Proportionality). On the first, it is not legitimate to use force against civilians and, even though some collateral civilian damage may occur, it is wrong to deliberately target non-combatants. On the second, combatants may only use the force necessary to achieve their ends -- the force used must be proportional to the ends that are to be secured in conducting the war. There are further requirements governing fairness, such as requirements to comply with international laws and treat prisoners fairly, but the two featured principles are the most commonly invoked in normative analyses of Jus In Bello.