The book rethinks the means of harmonization of prima facie norm conflicts in light of the multitude of international agreements across regimes. The methodology deployed in this book, which is referred to as complementation or complementary application, represents a novel approach by focusing on commonly shared objectives and a unifying ordre public transnational across fields of public international law that allow for a harmonization beyond traditional treaty interpretation. Fields of public international law, mainly the laws of armed conflict, international environmental law, and human rights law, apply simultaneously to questions regarding the environment and war. Such a coexistence challenges the unity of the international legal order, and it also challenges the means of harmonization across fields of public international law. However, eventually, the co-existence of several fields of public international law can result in a refinement of international law and enhanced legal protection. Diversification can also contribute to clarification or normative intensification in areas of parallel application of various fields and multilayered legal protection, demonstrating a counter-option to fragmentation.