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Welcome to the New Defense-Dominant World

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Argument

An expert’s point of view on a current event.

Welcome to the New Defense-Dominant World

As military power proves less effective, an old IR theory is making a comeback.

!Walt-Steve-foreign-policy-columnist20

*Walt-Steve-foreign-policy-columnist20*

*Stephen M. Walt*

By **Stephen M. Walt**, a columnist at *Foreign Policy* and the Robert and Renée Belfer professor of international relations at Harvard University.

!USA's goalkeeper Charlie Lindgren reacts during the IIHF Men's Ice Hockey World Championship quarter-final match between the United States and Czech Republic in Prague on May 23, 2024.

*USA's goalkeeper Charlie Lindgren reacts during the IIHF Men's Ice Hockey World Championship quarter-final match between the United States and Czech Republic in Prague on May 23, 2024.*

USA's goalkeeper Charlie Lindgren reacts during the IIHF Men's Ice Hockey World Championship quarter-final match between the United States and Czech Republic in Prague on May 23, 2024. Michal Cizek / AFP

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*

September 1, 2026, 10:18 AM

Russia’s ill-advised invasion of Ukraine and the United States’ equally stupid war with Iran suggest that we have entered a new world of “defense dominance,” a world where larger and more powerful states find it hard to conquer territory or to get much weaker states to make big concessions. United Nations Secretary-General António Guterres apparently thinks so, telling the *Financial Times*, “If you look at what happened in recent times, the capacity of superpowers to impose their will or their strength or their force in several situations has been severely limited.”

The proximate causes aren’t hard to identify—the development of sophisticated drones and accurate missiles, as well as improved surveillance and targeting capabilities that have made it harder for large units to operate in the open where they can be targeted by hidden defenders. Similarly, expensive power projection capabilities (aircraft carriers, stealthy aircraft, and the like) are becoming vulnerable to defenders and are having a lot of trouble trying to eliminate cheaper and easy-to-conceal drones and ballistic missiles. In the hands of a resolute enemy, these novel capabilities have made it easier for even comparatively weak adversaries to mount a potent defense of their home territory and even impose costs at a distance, which in turn makes it harder for objectively stronger powers to compel them to surrender.

Russia’s ill-advised invasion of Ukraine and the United States’ equally stupid war with Iran suggest that we have entered a new world of “defense dominance,” a world where larger and more powerful states find it hard to conquer territory or to get much weaker states to make big concessions. United Nations Secretary-General António Guterres apparently thinks so, telling the *Financial Times*, “If you look at what happened in recent times, the capacity of superpowers to impose their will or their strength or their force in several situations has been severely limited.”

The proximate causes aren’t hard to identify—the development of sophisticated drones and accurate missiles, as well as improved surveillance and targeting capabilities that have made it harder for large units to operate in the open where they can be targeted by hidden defenders. Similarly, expensive power projection capabilities (aircraft carriers, stealthy aircraft, and the like) are becoming vulnerable to defenders and are having a lot of trouble trying to eliminate cheaper and easy-to-conceal drones and ballistic missiles. In the hands of a resolute enemy, these novel capabilities have made it easier for even comparatively weak adversaries to mount a potent defense of their home territory and even impose costs at a distance, which in turn makes it harder for objectively stronger powers to compel them to surrender.

This situation could be especially challenging for the United States, which has grown accustomed to operating with near impunity against its adversaries and enjoying “command of the commons” from which it can project power against foes. True, these advantages didn’t enable the United States to defeat determined local adversaries—such as North Vietnam or the Taliban. But it did allow it to topple brittle and fragile autocrats like Saddam Hussein, Nicolás Maduro, and Muammar Gaddafi, as well as to win gross mismatches like the invasions of Grenada in 1983 and Panama in 1991.

The big question, however, is whether recent developments constitute a far-reaching shift in the efficacy of military power—the purposes for which it can be used successfully—and the broader character of international politics. As it happens, there is an extensive, if controversial, body of international relations theory that bears directly on this question, based on the simple but elusive concept of the “offense-defense balance.”

As developed by George Quester, Robert Jervis, Stephen Van Evera, Charles Glaser and Chaim Kauffmann, and others, offense-defense theory argues that the ease or difficulty of conquest could have profound effects on the security of states and how they related to each other. In brief, if conquest is easy, then all states are less secure by definition. Some will be tempted to try and expand, both because it is easier to do and because being bigger might improve their chances for long-term survival. Empires will be easy to acquire yet hard to maintain. Preemptive and preventive wars