The World Has Quietly Entered an Age of Defense Dominance

Stephen Walt argues in a new Foreign Policy essay that the wars in Ukraine and Iran have revealed a structural shift in the balance of power that most policymakers have yet to absorb: large, well-resourced militaries are struggling to conquer territory or coerce far weaker adversaries into concessions. He traces this to the maturing of cheap drones, precision-guided missiles and pervasive surveillance, which together make it costly for large mechanized units to mass in the open, exposing them to hidden, dispersed defenders. Russia's campaign against Ukraine and Washington's inconclusive confrontation with Iran both illustrate the same lesson: firepower advantages no longer translate into decisive territorial gains the way they once did. Walt cites UN Secretary-General António Guterres's observation that “the capacity of superpowers to impose their will…has been severely limited,” treating it as evidence the shift is now visible even to institutions built around great-power primacy. The implications cut against decades of Western defense planning premised on offense-dominant scenarios, from NATO's tripwire deployments to Beijing's Taiwan contingencies. If defense truly has the upper hand, Walt suggests, deterrence gets cheaper and invasion gets costlier for everyone — including states, like Russia, that assumed quick victories were still available. That logic recasts a string of stalled wars not as failures of will but as evidence of a more forgiving strategic environment for the weak, and it is exactly the kind of reframing that will keep shaping how officials in Washington, Warsaw and Beijing think about the next crisis.