Securing Ukraine May Require Western Forces

If the war in Ukraine winds down to a ceasefire, Kyiv may need Western combat power to insure its security. Lightly armed peacekeepers could not help Ukraine deter and defend against renewed Russian aggression. A better model may be the U.S.-led forces in South Korea, which like Ukraine faces a substantial hostile threat.

In 1953, the Korean War evolved into an armistice – an indefinite ceasefire. Both sides withdrew forces over a mile back from the ceasefire line. The armistice was put in place, but a “final peaceful settlement” was never achieved. To this day powerful U.S.-led United Nations Forces bolster South Korea’s defenses.  

The war in Ukraine could take a similar path. Ukraine will not formally cede territory to Russia, but President Volodymyr Zelenskyy has hinted at a temporary transfer if Ukraine receives a “NATO umbrella.” But in part because President-Elect Donald Trump opposes this step, Ukraine is unlikely to join NATO anytime soon. 

Instead, like South Korea, Ukraine might best focus on maintaining a strong military and encouraging the West to deploy a combat force in Ukraine that can help it deter and defend against an unrepentant aggressor.

The threat from Russia may be so great that United Nations Forces in South Korea – including over 28,000 U.S. troops – might be a better model for what Ukraine needs. A 60,000-troop NATO Implementation Force (IFOR) was established in Bosnia and Herzegovina after conclusion of the 1995 Dayton peace accords even though it did not face a large-scale invasion threat.

A core U.S. force element anchoring a larger multinational coalition could reassure Ukraine and its partners. Several options are possible.

One might be a battalion-sized Western force. After Russia’s 2014 invasion of Ukraine, NATO put battalion-sized (1,000-or-so troops) multinational battlegroups in Poland and each Baltic state. A “tripwire” force of this size alone may not be enough to help deter an attack.

A second option might add a U.S. Army Prepositioned Stockpile (APS). Such sets of equipment, including the tanks and wheeled vehicles for an armored brigade combat team (BCT), are strategically prepositioned abroad. In a contingency, an APS could enable a larger U.S. and allied contingent to surge quickly into Ukraine. The “tripwire” force might protect this operation.

A third option might elevate the Western presence in Ukraine to a brigade-sized force. Germany and Italy each host a U.S. Army BCT, which has 4,000-4,700 troops. A BCT-sized force in Ukraine could organize an additional division or two of reinforcing Western forces. Following Russia’s full-scale invasion of Ukraine in 2022, NATO upgraded battlegroups in Poland and each Baltic state to brigade-sized. A BCT-sized force in Ukraine would be only a quarter of the size of U.S. forces in South Korea.

A Western force in Ukraine might best operate under NATO command, but there are other precedents. The U.S.-led coalition to counter the Islamic State in the Levant in Iraq and Syria had 87 members. In 2004, the European Union took over a NATO peacekeeping mission in Bosnia-Herzegovina that had kept the country safe for nine years after the war ended. Since Ukraine borders on four NATO members and the alliance now chairs the 57-member Ukraine Defense Contact Group, NATO command could be the most effective. 

If the present war leads to a ceasefire, Ukraine may emerge as a premier European land power by size and by dint of having fought off Russia’s larger forces to a near stalemate for almost three years. Western forces complementing Ukraine’s would be a force multiplier not just for Ukraine’s security, but for security of NATO’s eastern flank and the broader Black Sea region.

William Courtney is an adjunct senior fellow at the RAND research institution and was the U.S. ambassador to Kazakhstan, Georgia, and the U.S.-USSR commission to implement the Threshold Test Ban Treaty.

Michael Cecire is a policy researcher at RAND and was a senior policy advisor and staff political-military officer at the U.S. Commission on Security and Cooperation in Europe (Helsinki Commission).

John Hoehn is a policy researcher at RAND and a former military analyst with the Congressional Research Service.

Hunter Stoll is a defense analyst at RAND and an Army Reserve intelligence officer.