The recent conclusion to the war in Afghanistan - America's longest and one of its most frustrating - serves as a vivid reminder of the unpredictability and tragedy of war. In this timely book, esteemed military expert Michael O'Hanlon examines America's major conflicts since the mid-1800s: the Civil War, the two World Wars, Korea, Vietnam, Iraq, and Afghanistan. O'Hanlon addresses profound questions. How successful has the United States been when it waged these wars? Were the wars avoidable? Did America's leaders know what they were getting into when they committed to war? And what lessons does history offer for future leaders contemplating war?-including the prospects for avoiding war in the first place. Certainly, Vladimir Putin should have thought harder about some of these questions before invading Ukraine. O'Hanlon looks for overarching trends and themes, along with the lessons for the military strategists and political leaders of today and tomorrow. His main lessons include the observations that war is usually far more difficult than expected, and that its outcomes are rarely predictable. O'Hanlon's unique book - combining brevity and clarity with a broad conceptual approach -is an important for students of security studies at universities and war colleges as well as generalists.