This study examines the causes, consequences, and possibilities of war prevention from the perspective of international relations theories (realism, liberalism, and constructivism). The study answers the question: Why do states enter war, and which theories can best explain it? This study is a qualitative analysis that provides a comparative assessment of international relations theories. Academic articles, and books were used for the study. Qualitative content analysis and comparative analysis are the main methods of this study. The study showed that each theory offers a unique analysis of war: Realism considers war to be the result of power competition, the anarchy of the international system, and the self-preservation policies of states. Liberalism believes that economic cooperation, democracy, and international organizations can prevent war. Constructivism views war as a result of the identities, values, and perceptions of states. The results show that no single theory can provide a comprehensive analysis of war, but realism provides the most practical framework. No single theory can explain all the causes of war, so a combination of different theories is needed. Realism prioritizes the balance of power, liberalism emphasizes the importance of economic cooperation, and constructivism emphasizes the role of identities. States should use a combination of balance of power (realism), economic cooperation (liberalism), and mutual understanding (constructivism). International organizations should be strengthened to prevent war. The analysis of international relations should be expanded to include cyber-war, terrorism, and unconventional warfare.