Barry Posen | Survival: Global Politics and Strategy & International Institute for Strategic Studies (IISS)
October 8, 2025
From the latest issue of Survival: Global Politics and Strategy, Barry Posen, professor of political science, writes, “worst-case assumptions can as easily paralyse as mobilise, but Europe should at least start with bad-case assumptions: an unreliable United States and Russia’s prompt recovery from its Ukraine exertions."
Abstract
European defence planners must now work with ‘bad-case’ assumptions: a United States that is less reliable, and a Russia that recovers from its Ukraine exertions earlier and more robustly than its poor wartime performance and slowing economy might suggest. In the short term, to deter and defend against future Russian moves, planners must extract maximum combat power from the force structure they have. They should be guided by the old concept of the ‘mass of manoeuvre’ – that is, a large force that can be dispatched quickly for maximum effect on Russian decision-making. The force, which would require both a ground and an air component, should be assembled in a time of crisis in Poland owing to its size, location and transportation connections to the west. A ten-brigade NATO force reinforcing the 14-brigade Polish army would make Poland an exceptionally hard target, with forces comparable to those Ukraine mounted to thwart Russia’s offensive in early 2022. The very existence of such a force would severely complicate any aggressive Russian plans in Central and Northern Europe.
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