The Prohibition of the Use of Force in Practice (1945–2020): Justifications, Contestations, and International Reactions

Abstract How has the jus contra bellum operated and performed in state practice since the establishment of the UN Charter? This article presents a precise account based on an evaluation of an original dataset produced for the purposes of the present research project. The article builds on the structured analysis of how international law has been used to justify, evaluate, and criticize uses of force in 81 major armed conflicts fought between 1945 and 2020. First, we establish whether, to what extent, and how given actors have justified their participation in armed conflicts as well as what legal grounds have been invoked. Second, we explore exactly what it is that various actors have contested in practice (eg, the facts, the application of the law, the validity of rules, new justificatory grounds) and draw conclusions about the effects of these legal disputes on international law. Third, we assess how international actors – that is, UN organs as well as states – have reacted to military interventions and accompanying legal justifications. Via a detailed analysis of how the jus contra bellum operates as a conflict-driven order, the article develops a nuanced understanding of the functioning and limits of this order. It furthermore provides proof and concrete numbers concerning some commonly held views, such as views about states’ general affirmation of international law as the only relevant justificatory system in use thus far. The article simultaneously debunks some commonly held views, such as the assumption that the jus contra bellum is a particularly dynamic order in which legal change is regularly triggered by states’ legal claims. Moreover, the article additionally explores current sources of threats to the law against war. The obtained data demonstrate that – as well as how – the law against war operates as a stable legal order, with dynamic elements only occasionally occurring in a few substantive areas. The article builds on and is accompanied by original data, including extensive case studies and statistical evaluations, which can be accessed online and used in further research.