Barry R Posen in his essay Putin’s Preventive War: The 2022 Invasion of Ukraine’ Published in International Security (Winter 2025) argues that Russia invaded Ukraine in 2022 to prevent a future shift in the balance of power, not as a bid for imperial expansion.
Posen contends that Russian leaders perceived Ukraine’s growing military strength and closer ties with NATO as a looming window of vulnerability—a future in which Russia would face greater security threats and reduced strategic leverage. At the same time, Russia also saw a window of opportunity—a short-term chance to act while its military strength was still sufficient to alter the strategic balance in its favor.
Posen’s study highlights that states engage in preventive wars when they anticipate a shrinking ability to act effectively and fear long-term decline. Evidence from Russia’s military actions and diplomatic exchanges supports this view. His work calls for further research into how perceptions of vulnerability and opportunity shape state behavior and how deterrence strategies should be adjusted accordingly.
Posen argues that this framework explains why Putin chose to invade Ukraine in 2022 despite the high military and political costs. Evidence from Russian military actions and diplomatic exchanges supports this view.
These insights are especially relevant beyond Ukraine. The United States faces a similar challenge with China and Taiwan. U.S. efforts to bolster Taiwan’s defenses and strengthen regional alliances aim to deter Chinese aggression, but they also risk reinforcing China’s fears of a shifting balance of power. The U.S. and its allies must be mindful that their deterrence measures do not inadvertently create the conditions for a preventive war.
Realist theory predicts the occurrence of preventive wars, and Russia’s actions align with this logic. The failure of Western powers to calibrate their support for Ukraine while addressing Russian security concerns contributed to the conditions that led to war.
