The purpose of this work is to trace the processes that led and continue to lead to the formation of the treaty norms applicable in non-international armed conflicts. If the purpose of humanitarian law is to achieve a balance between military necessity and humanitarian considerations and to prevent unnecessary suffering and destruction, humanitarian law rules should be equally applicable to both international and internal armed conflicts. Whilst, however, there are a huge number of treaty provisions applicable to international armed conflicts, very few provisions are specifically designed to regulate non-international armed conflicts despite the dramatic increase in the number of such conflicts. The study investigates the reasons behind the differences by analysing, inter alia, questions such as: Where does the international law of internal armed conflicts come from? Why did it evolve differently from the law regulating international armed conflicts? Where is the international law of internal armed conflicts going?