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 Military History for the Modern Strategist: America's Major Wars Since 1861 (Brookings, 2023), 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.

Michael E. O’Hanlon is a senior fellow and director of research in Foreign Policy at the Brookings Institution, where he specializes in U.S. defense strategy, the use of military force, and American national security policy. He directs the Strobe Talbott Center on Security, Strategy and Technology, as well as the Defense Industrial Base working group, and is the inaugural holder of the Philip H. Knight Chair in Defense and Strategy. He co-directs the Africa Security Initiative as well. He is an adjunct professor at Columbia, Georgetown, and George Washington universities, and a member of the International Institute for Strategic Studies. He also serves as a member of the Defense Policy Board at the U.S. Department of Defense.

Sam Canter is a policy and strategy analyst, PhD candidate in Politics and International Relations, and Army Reserve intelligence officer. He previously served on active-duty as both an Infantry and Military Intelligence officer, and as a civil-servant at the White House. His views are his own and do not reflect any institution, organization, or entity with which he is affiliated.