In legal discourse, culture matters. The current debate an the international use of force experiences a transatlantic divide between the US and Continental Europe. This divide can be explained by the fragmentation of legal culture. Continental-European civil law and US common law culture fundamentally differ with regard to the role of the judicial process, the method of legal reasoning, the general paradigm of legal analysis, the value of neutrality, and the required degree of formalism. In the field of the international use of force, cultural differences shape international legal discourse an a theoretical and on a methodological plane. Traditionalist theories and methodologies are shaped by a Continental-European civil law culture. Reality-oriented theories and methodologies are informed by US common law culture. Natural law-based approaches reflect a civil law culture on the theoretical, a US common law culture an the methodological plane. These cultural differences prejudice legal opinions on the legality of international forceful action, catalyze opposing views as to the continued validity of the UN Charter system, and accommodate opposing worldviews on the role of international law in international relations. To bridge the transatlantic divide, international lawyers must adapt their argumentative style to the cultural conventions of their transatlantic audience.