In late February, Russia’s war against Ukraine entered its fifth year, and a few days later, the United States and Israel launched massive air strikes on Iran. In addition, European and Asian states are now arming up at the fastest rate since the Cold War, and a war between the United States and China over Taiwan remains a real possibility. Against this dark background, it is important to revisit long-standing discussions about how military power should be applied to achieve strategic goals; how to measure and judge military power accurately; and what factors beyond military force may influence the outcome of war.

One excellent contribution to this debate is a recently published book by Phillips Payson O’Brien. In War and Power: Who Wins Wars—and Why, O’Brien, who is a professor of strategic studies at the University of St Andrews in Scotland, reminds us that the outcome of war may indeed be influenced by aspects beyond guns, air power, and the number of soldiers. He argues that a more holistic approach to how military might is usually measured will improve our understanding of who wins wars and why—and potentially even deter states from going to war in the first place.

In late February, Russia’s war against Ukraine entered its fifth year, and a few days later, the United States and Israel launched massive air strikes on Iran. In addition, European and Asian states are now arming up at the fastest rate since the Cold War, and a war between the United States and China over Taiwan remains a real possibility. Against this dark background, it is important to revisit long-standing discussions about how military power should be applied to achieve strategic goals; how to measure and judge military power accurately; and what factors beyond military force may influence the outcome of war.

One excellent contribution to this debate is a recently published book by Phillips Payson O’Brien. In War and Power: Who Wins Wars—and Why, O’Brien, who is a professor of strategic studies at the University of St Andrews in Scotland, reminds us that the outcome of war may indeed be influenced by aspects beyond guns, air power, and the number of soldiers. He argues that a more holistic approach to how military might is usually measured will improve our understanding of who wins wars and why—and potentially even deter states from going to war in the first place.

War and Power: Who Wins Wars—and Why, Phillips Payson O’Brien, PublicAffairs, 288 pp., $30, October 2025

O’Brien starts the book by examining the false but widespread prediction of a quick Russian victory against Ukraine in 2022. Not only Russian President Vladimir Putin but the vast majority of Western politicians, analysts, and commentators overestimated Russian military power and underestimated that of Ukraine. The book was written and published before the recent U.S.-Israeli strikes on Iran, but given O’Brien’s take on the United States’ attempts at regime change in Iraq and Afghanistan, it is probably fair to assume that he would have advised Washington not to undertake a similarly overconfident endeavor in Iran. The book ends with a stark warning to Beijing and Washington not to start a cataclysmic war based on misperceptions about each other’s military capabilities.

The book engages with the topic of war and power in five main ways.

First, it takes a broad swing at the ineptness of governments, intelligence communities, and academia in assessing military power and predicting the outcome of war. O’Brien notes that due to the complexity of factors involved, wars seldom develop as planned and often go off the rails, lasting much longer than the aggressor anticipates. The author argues that one of the most fundamental problems in the analysis of war is the tendency to focus on battles, with wars unfolding in a much larger and more complex context than single battles or aerial bombing........

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