This research examines the relationship between war and peace within the realm of international relations, drawing from a diverse array of theories. It investigates conflict, ranging from power dynamics to ideological disputes, while also evaluating the ethical dimensions of the Just War theory. Through the application of the Just War theory to the dynamic interplay between war and peace as a theoretical framework, this study underscores the vital significance of fostering peaceful dispute resolution, upholding ethical standards in warfare, and undertaking comprehensive post-conflict reconstruction efforts. Employing a historical research design, the study gathers data from secondary sources including journals, books, and ancient encyclopedias, ensuring the credibility of its analysis. Utilizing a descriptive method of data analysis, the research employs deductive logic to maintain a coherent framework and ensure balanced interpretation. Despite disagreements among theories, the study prioritizes accuracy to draw appropriate conclusions. The findings of this study reveal the profound interconnectedness between war and peace, highlighting how conflict arises from a myriad of factors including power struggles, ideological differences, and diplomatic failures. Furthermore, the ethical evaluation of war through the Just War theory provides valuable insights into the moral complexities surrounding armed conflict and its implications for peace-building efforts. Considering these findings, several recommendations are proposed to address the persistent challenge of achieving lasting peace amidst armed conflicts. Emphasizing diplomacy as a primary approach to conflict resolution, prioritizing ethical standards in warfare, and fostering peace education to cultivate values of tolerance and non-violent conflict resolution from an early age are key strategies identified for promoting sustainable peace. By offering recommendations for proactive conflict prevention and strategies in international cooperation, this research aims to contribute to the global pursuit of a more equitable, harmonious, and peaceful world order. Through its rigorous analysis and actionable insights, the study seeks to inform policymaking and advocacy efforts aimed at fostering sustainable peace on a global scale.