The Vietnam War is one of the longest and most controversial in US history. This book seeks to explore what lessons the US military took from that conflict as to how and when it was appropriate for the United States to use the enormous military force at its disposal and how these lessons have come to influence and shape US foreign policy in subsequent decades. In particular this book will focus on the evolution of the so called 'Powell Doctrine' and the intellectual climate that lead to it. The book will do this by examining a series of case studies from the mid-1970s to the present war in Afghanistan.