Humanitarian Intervention and Unilateral Use of Force without UN Security Council Authorization: Assessing the Emergence of Customary International Law in the Context of U.S.-Israeli Military Action Against Iran (2026)

Abstract

The prohibition on the use of force under the UN Charter remains a cornerstone of international law, yet debates over unilateral humanitarian intervention persist, particularly in cases lacking UN Security Council authorization. Recent military actions, including the 2026 U.S.–Israeli operation against Iran, have intensified questions about whether state practice is reshaping customary international law. This study aims to assess whether the 2026 intervention can be legally justified under existing jus ad bellum principles and to evaluate whether it contributes to the emergence of a customary rule permitting unilateral humanitarian intervention without Security Council approval. The research adopts a qualitative doctrinal-empirical design, combining legal analysis of treaty law, International Court of Justice jurisprudence, and principles such as necessity and proportionality, with structured content analysis of 113 documents, including state statements, UN records, and legal commentaries. Data are coded to identify patterns of state practice and opinion juris using the International Law Commission’s two-element test for customary international law. Findings indicate that a majority of states reject the legality of the intervention, reaffirming the centrality of Article 2(4) and the requirement of Security Council authorization. Support for unilateral humanitarian justification is limited, regionally concentrated, and doctrinally inconsistent. While some states invoke self-defense or humanitarian reasoning, the overall pattern reflects legal contestation rather than convergence toward a new customary norm. The study concludes that no clear customary international law exception permitting unilateral humanitarian intervention has emerged. The UN Charter framework remains dominant, and legal evolution in this domain is constrained by widespread state resistance. The findings underscore the need to strengthen collective mechanisms for civilian protection rather than expand unilateral uses of force.