The Demographic Dilemma: Why Military Support Must Consider Population Trends

Commentary by Benjamin Jensen and Mark Montgomery

Published December 16, 2024

This series-led by the Futures Lab and featuring scholars across CSIS-explores emerging challenges and opportunities likely to shape peace negotiations to end the war in Ukraine. All contributions in the series can be found by visiting Strategic Headwinds: Understanding the Forces Shaping Ukraine's Path to Peace.

The strategic center of gravity for Ukraine in its war with Russia is its ability to sustain the manpower needed to man the front lines against a determined foe. Ukraine has struggled to mobilize enough of its population to man trench lines across its frontier, partially out of fear of sacrificing future generations. These manpower challenges will not end with the war. As a result, Kyiv's backers must signal a willingness to bolster its mobilization capacity after the conflict ends. Doing so will strengthen Ukraine's negotiation position and ensure any settlement addresses larger European security concerns.

Baby Bust

Ukraine entered the war with a challenging demographic outlook that limited its ability to forcibly conscript large numbers of young men and women as the war progressed. Population growth was already declining due to migration and lower birth rates. The war compounded the problem, with over 14 million people-almost a third of the population, forced to flee their homes, according to the International Organization for Migration. Now, UN reports estimate the population could drop further over the coming decades. There were almost 50 million Ukrainians in 2000, and the World Health Organization projects that to collapse to 32 million by 2050.

These bleak demographic trends have limited the ability of Kyiv to mobilize the population. There are also almost three times as many Ukrainians over 65 as there are under 14, forecasting further risks of mobilizing what has traditionally been seen as the "military age" to fight future wars. As a result, it took Ukraine two years to lower the mobilization age from 27 to 25 years old.

The problem is not confined to Ukraine. Other frontline democracies face a similar challenge. Taiwan has extended mandatory conscription from four months to one year but is facing one of the world's lowest birth rates of 1.09 children per woman. This trend will leave the island with 20,000 fewer births by 2035 compared to 150,000 in 2021. South Korea is facing a demographic-driven recruitment shortfall compounded by declining interest in military service at the same time, the threat from North Korea is increasing. Applications to military academies are dropping, and the Army is struggling to recruit and retain enough noncommissioned officers. Japan faces similar challenges. In 2024, the Japanese Self-Defense Forces recruited just 51 percent of the annual goal to maintain the required number of service men and women required to defend the nation.

To offset the demographic decline, states have to either make concessions or pay more to attract citizens to serve. Israel, which relies on a large reserve, had to overturn a long-time religious exemption for the ultra-orthodox Haredi community due to the strains of a multifront, protracted war. Even autocracies like Russia have had to take extraordinary actions, they have avoided mobilizing young men from wealthier areas and paid their butcher's bill through recruiting prisoners, foreigners, and minorities and via exorbitant payouts for volunteers leading to what one analyst labeled "deathonomics," a situation in which a person is worth more dead than alive skewing rational choice.

Building Mobilization Capacity to Support Negotiations and Deterrence

These broader demographic trends highlight a critical challenge for democratic states engaged in protracted conflicts while seeking to deter regional adversaries: the need to expand mobilization capacity. Military power is not solely determined by the quantity of tanks, planes, or ships a state can field. Rather, it hinges on the ability to mobilize populations and scale industries to sustain and generate combat power over time.

In the context of any negotiations to end the war in Ukraine, this dynamic will play a pivotal role. Moscow's assessment of Ukraine's resilience will extend beyond the immediate battlefield. It will evaluate the long-term balance of forces and means-projecting how relative military and industrial capacities might evolve over the next decade. This strategic calculus will shape Russia's negotiating position, emphasizing the importance of demographic and industrial resilience as determinants of power in modern conflicts.

Understanding these broader factors is essential for policymakers and strategists involved in conflict resolution and designing campaigns to deter future wars. They underscore that the outcome of war is not just decided by current capabilities but also by a state's ability to sustain and adapt its power over time.

To strengthen Ukraine's mobilization capacity and bolster Kyiv's position in any potential negotiations, the United States and its partners can focus on two key areas: reinforcing the social contract of service and committing to long-term training initiatives.

First, military service is fundamentally a social contract, even for conscripted soldiers. To sustain morale and incentivize service, there must be clear, tangible rewards for those who sacrifice. This requires a robust, long-term investment in veterans' programs. In the United States, this has evolved into benefits such as first-time homebuyer assistance, small business loans, education opportunities, and healthcare. These programs not only strengthen the social fabric that underpins military service but also contribute to Ukraine's post-war reconstruction. Importantly, they provide a nonlethal avenue of support that could attract contributions from partner states hesitant to provide direct military aid.

Second, the United States and NATO must signal a lasting commitment to training Ukrainian forces. Combat power is not merely a function of manpower; it is amplified by the quality of training. Well-trained soldiers generate significantly greater battlefield effectiveness. A long-term "advise and assist" mission-encompassing basic training, operational art, and advanced planning-will ensure Moscow recognizes that Ukraine's military capability will continue to grow, even beyond the immediate conflict. This dual approach aligns military readiness with societal resilience, sending a clear signal to Moscow about Ukraine's enduring capacity for self-defense.

As the war in Ukraine continues to reshape the geopolitical landscape, the ability to mobilize and sustain combat power will remain a decisive factor in shaping Kyiv's position at the negotiating table. By reinforcing the social contract through robust veterans' programs and committing to a long-term training mission for Ukrainian forces, the United States and its partners can help ensure that Ukraine is not only equipped to defend itself today but also positioned to deter future aggression. These efforts will signal to Moscow and the international community alike that Ukraine's resilience is both strategic and enduring, laying the groundwork for a just and sustainable resolution to the conflict.

Benjamin Jensen is a senior fellow in the Futures Lab at the Center for Strategic and International Studies in Washington, D.C. Rear Admiral (ret) Mark Montgomery is the senior director in the Center on Cyber and Technology Innovation at the Foundation for Defense of Democracy.

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