Abstract The renewed escalation of tensions in the Middle East during the 2026 Iran crisis has revived a fundamental debate in international security and ethics: whether peace is best preserved through legal restraint or through military strength. This paper examines the concepts of pre-emptive and preventive war within the framework of international law and the theological tradition of Just War and Just Peace. The paper analyzes the legal limits of anticipatory self-defence in jus ad bellum, including the principles of necessity, imminence, and proportionality associated with the Caroline doctrine. It then engages the ethical perspective of Christian thought, particularly the transition from classical Just War theory to the modern theology of Just Peace. Drawing on the natural law tradition and the philosophical reflections of Dietrich von Hildebrand, the paper argues that law and moral order must guide the use of force rather than be subordinated to strategic calculations of power. Using the 2026 Iran crisis as a case study, the paper evaluates the legal and moral arguments used to justify anticipatory military action. It argues that while narrowly defined pre-emptive self-defence may be compatible with international law under strict conditions of imminence, preventive war undermines both the legal framework of the United Nations system and the ethical foundations of a just peace. The study concludes that a sustainable international order requires reinforcing the primacy of law and moral norms while addressing legitimate security concerns through collective institutions and diplomacy. Outlook 1. Introduction 2. International Law and the Use of Force 3. Pre-emptive vs Preventive War 4. Natural Law and the Theology of Just Peace 5. Case Study and Conclusion: The 2026 Iran Crisis