 When trying to understand the laws that regulate armed conflicts, we often encounter two terms that tower over the subject use ad bellum and use in bello use ad bellum Latin for the law on going to war refers to the conditions under which states may resort to the use of force Use in bello Latin for the law in war refers to the norms governing behavior in armed conflicts while they are actually happening So while both use ad bellum and use in bello deal with matters linked to armed conflict, they refer to different branches of law Use ad bellum is another term for the international law regulating the resort to force by states This law determines whether such use of force is legal or not Article 2 section 4 of the United Nations Charter States All members shall refrain in their international relations from the threat or use of force against the territorial integrity or Political independence of any state or in any other manner inconsistent with the purposes of the United Nations Exceptions to this prohibition are self-defense and authorization by the UN Security Council Use in bello is another term for international humanitarian law IHL IHL does not rule on whether an armed conflict is legal or not. That is not relevant for IHL Instead it sets clear rules for whenever there is an armed conflict These rules are laid down notably in the 1949 Geneva conventions their additional protocols and customary IHL for international and non-international armed conflicts They regulate matters ranging from the treatment of the wounded to the prohibition of attacks against civilian populations IHL applies to all parties to an armed conflict irrespective of the reasons for fighting Irrespective of who might be considered to be entitled to use force and irrespective of lawfulness or unlawfulness under the use ad bellum So the difference between these two terms should be clear Use ad bellum the international law regulating the resort to force by states use in bello IHL a pragmatic set of rules that states have developed and agreed to for governing behavior in all armed conflicts As long as armed conflicts take place IHL is there to uphold the fundamental tenets of humanity even in the midst of fighting