The research project questions the linear-progressive narrative of legal development that still prevails in contemporary IHL and proposes a new history of the European laws of war in the 19th century. Instead of simply declaring them the "precursor" of modern IHL, the project examines the central codification events of the 19th century in their socio-historical and geopolitical context. Contrary to classical accounts, the focus is not on the development towards a certain future vanishing point, but on the function of the laws of war in a Europe understood as a peculiar legal space. To this end, the project elaborates the ideological-historical foundations and modes of operation of post-Napoleonic European international law. It shows how the contingent transition from the princely state to the nation-state caused an increasing displacement of the originally at least partially existing will of princes for cooperation by the willingness of nations for confrontation. Against the background of this socio-historical phenomenon, the laws of war and their codification have an original peace-securing function: When, after a period of peace lasting about forty years, the Crimean War of 1853 led to the first European war between the Great Powers, it was due to the special state interests of Prussia and Austria that the conflict did not escalate into a "general" or "great war. However, since the European balance would thus not be able to secure peace in Europe in the long run, the state interest shifted from preventing the war to limiting its execution. As a "continuation of politics by other means," war in Europe was also to follow the rules of a well-understood political interest. Due to its fundamentally destabilizing effect, it should not only be ended as soon as possible, but at the same time establish a more stable peace, which is why the work understands the law of war as an original European special law. In this context, the project pays special attention to revealing the special state interests regularly hidden behind the legal concepts of "military necessity" and "considerations of humanity."