Discover the complexities of the Afghanistan War, the United States’ longest military operation and a conflict with far-reaching impacts in Afghanistan and around the globe. In this accessible ready-reference encyclopedia, more than 150 entries highlight key people, groups, battles, and concepts and provide valuable insights into the causes, course, and legacy of this lengthy conflict. Cross referencing and further readings accompany each entry, helping readers make connections and pointing them toward resources for additional study. The main text is complemented by a chronology that provides an at-a-glance overview of important events, allowing readers to trace the evolution of the invasion and occupation of Afghanistan. The 2001 U.S.-led war in Afghanistan, launched in response to 9/11, aimed to dismantle Al-Qaeda and topple the Taliban regime. While the initial invasion achieved these goals, the war transformed into a long and costly struggle against insurgents. Despite efforts to build a new Afghan state, the conflict quickly became a stalemate. The 2021 withdrawal by the United States and NATO and the subsequent return to power of the Taliban ended a war with a complex legacy. The protracted conflict reshaped the United States’ role in the world, highlighted the challenges of nation-building, and has left the future of Afghanistan uncertain.