This study adopts an analytical–comparative approach to examine the legitimacy of the use of force under two legal systems: contemporary international law and Islamic jurisprudence. The main objective is to identify the similarities and differences between these systems in determining the conditions and limits for the lawful use of force. The research method is descriptive–analytical, relying on library sources, international legal instruments, and authoritative Islamic legal texts. The findings indicate that both systems consider peace as the norm and war as an exception, permitting the use of force only under specific and restricted circumstances. In international law, such restrictions are primarily implemented through institutional mechanisms, such as the United Nations Security Council and the International Court of Justice. In Islamic jurisprudence, the legitimacy criteria are grounded in ethical principles, divine intention, and lawful leadership. The study concludes that combining the institutional efficiency of international law with the ethical depth of Islamic jurisprudence can provide a more comprehensive framework for regulating and legitimizing the use of force, thereby contributing to the promotion of a just and lasting international peace.