Purpose: This study seeks to assess the adherence to international law in the 2001 U.S.-led military intervention in Afghanistan, prompted by the September 11 attacks. Additionally, it aims to investigate the impact of the Greater Middle East Initiative on U.S. policy towards the Islamic World, specifically Afghanistan, providing insights into legal intricacies and broader consequences. Theoretical Framework: This article engages in discussions among Western scholars on the Afghanistan war and U.S. military involvement but distinguishes itself by incorporating insights from Middle Eastern scholars. It aims to enrich the discourse by integrating perspectives from within the Middle Eastern scholarly community, offering a comprehensive view of these complex subjects. Methodology: Employing historical, descriptive, and in-depth analytical research methods, this study examines events around September 11, 2001, providing essential context for the subsequent U.S. military intervention. Descriptive methods offer a detailed account of the post-9/11 shift in U.S. policy, while in-depth analytical methods scrutinize legal dilemmas arising from the intervention, contributing to a comprehensive understanding of historical context, U.S. policy decisions, and legal complexities. Results: The results and discussion section explores the historical evolution of U.S. military engagement in 21st-century Afghanistan, analyzing its strategic shifts and the Taliban's adaptation to guerrilla warfare. It critically evaluates the international legal aspects of the Afghan War, assessing the legitimacy of the U.S.-led military intervention based on UN conventions, historical precedents, and key principles such as the right to legitimate defense, urgency, and proportionality. Conclusions: The aftermath of September 11, 2001, marked a transformative moment in U.S. policy towards Afghanistan and the broader Middle East, leading to the consequential Afghan War. Despite its geopolitical significance, the absence of explicit UN Security Council authorization prompts a critical examination of the war's legitimacy, revealing lapses in meeting criteria for the right to individual or collective legitimate defense and urging a reevaluation of established narratives in international relations and global politics.