PREPARING FOR THE LONG WAR / GEOPOLITICAL FUTURES

Preparing for the Long War

Europe has come to understand the importance of wartime endurance.

By: Andrew Davidson

Russia’s invasion of Ukraine forced European governments to confront a problem they long thought obsolete: sustaining manpower in prolonged, high-intensity war. 

At the outset of the conflict, Ukrainian and Russian armed forces were structured for rapid campaigns. 

As casualties mounted, experienced and professionally trained personnel were lost faster than they could be replaced, so both sides had to expand their mobilization efforts. 

They soon learned that, if optimized for short operations, even large standing forces will struggle to absorb sustained losses without deep and functional reserve systems.

It seems the rest of Europe has learned this lesson, too. 

France has expanded operational reserve targets; Poland is enlarging active and territorial components; Germany is debating service reform amid recruitment constraints; and the United Kingdom has widened recall eligibility within its strategic reserve. 

That’s not to say this is a return to mass conscription. 

But it is to say that militaries understand that if they can’t win the short game, they better be able to win the long game.

Endurance requires manpower replacement, industrial sustainment and political tolerance. 

States do not always choose when wars begin or how long they last, but they can control how much military capacity they maintain in peacetime. 

That choice is constrained by threat perception, financial cost, political capital and signaling risk. 

(Expanding standing or reserve forces may deter adversaries, but it can also come off as offensive.) 

The challenge, then, is not simply determining how big your military needs to be in peacetime but ensuring that it can replace and replenish once attrition begins.

Personnel Layers in Modern War

Modern militaries manage manpower through layered systems designed to balance effectiveness, legitimacy and economic stability. 

Under prolonged conflict, how these layers function determines whether a military can absorb attrition. Standing forces constitute the first layer. 

They are immediately available, highly trained, optimized for rapid response and very expensive. 

Though they are decisive in the opening phase of conflict, standing forces alone lack the depth required to absorb sustained losses.

Reserves are the second and most consequential layer. 

Properly structured reserves provide qualitative continuity and quantitative depth, allowing states to rebuild combat power while preserving professional standards. 

Their effectiveness depends not only on numbers but also on training frequency, administrative readiness, legal call-up authority and integration with active formations and commands.

The third layer is population mobilization. 

When reserves are insufficient or poorly prepared, states draw directly from civilians. 

This expands manpower but is economically disruptive and politically risky. 

As force quality declines and coercion increases, mobilization begins to generate strain beyond the battlefield.

Russia entered 2022 with an active military of roughly 900,000 personnel and deployed an initial invasion grouping in Ukraine widely estimated at 150,000-200,000 troops. 

Following heavy losses and another mobilization of reservists, Russian force levels expanded significantly; estimates from the International Institute for Strategic Studies put active Russian military at over 1.1 million personnel. 

Ukraine evolved from a prewar active force of roughly 200,000 to approximately 730,000 active personnel by 2025, also according to IISS, with total security forces exceeding that figure if paramilitary units are included. 

In both cases, manpower expanded faster than specialists could be trained, resulting in a higher number of less professionalized troops. 

And because casualties are so high – in the hundreds of thousands per open-source estimates – that trend became harder to reverse.

In this case, the ability to restore lost capability proved more decisive than raw manpower. 

Which makes sense: Once wars exceed planning assumptions, mobilization is constrained less by how many people a state can summon than by how quickly it can train, equip, integrate and sustain them. 

The first binding constraint in this process is training throughput. 

Instructor availability, facilities and training infrastructure scale far more slowly than intake. 

As casualty replacement accelerates, training quality degrades and specialist replacement slows. 

Once lost, elite capability can’t be reproduced quickly.

Closely linked is infrastructure elasticity. 

Mobilization assumes available capacity in housing, medical facilities, logistics nodes and training grounds that rarely exist at the necessary scale. 

Under modern persistent intelligence, surveillance and reconnaissance, and precision strike conditions, these facilities are also vulnerable. 

Interwar mobilization models assumed warning time; contemporary surveillance and long-range strike capabilities compress that window, increasing the chances of mobilizing under fire.

Equipment and ammunition impose additional constraints. 

Even where industrial capacity exists, battlefield consumption tends to outpace production cycles. 

Accelerated wear, maintenance backlogs and training stock depletion create bottlenecks that limit field deployment and force training.

As mobilization continues, economies must be able to absorb the cost. 

Removing working-age cohorts from civilian employment necessarily strains economies. 

High-readiness reserve systems compress activation timelines but concentrate economic disruption in the early phases of conflict. 

This means that, ultimately, political tolerance becomes another constraint. 

Repeated call-ups, sustained casualties and perceptions of unequal burden distribution erode government legitimacy. 

Mobilization falters not when manpower pools are exhausted, but when the political system can no longer sustain the demands of replacement.

Comparing Models

This dynamic clarifies an often misunderstood distinction in modern mobilization between additive and substitutive reserve architectures. 

The United States’ Total Force model embeds critical functions – logistics, medical support, intelligence, cyber and key combat enablers – within reserve components. 

This allows lost capability to be restored qualitatively, not numerically. 

The system relies on deep civil-military integration, employer accommodation and standing administrative readiness that reduces mobilization lag while preserving technical proficiency. 

It does not eliminate sustainment limits, but it does delay capability degradation. 

(It also relies heavily on employer compliance and civil-military integration, both of which can suffer under prolonged mobilization.)

Israel, which maintains mandatory conscription followed by extended reserve obligations, represents a different but equally substitutive model. 

Its reserve system is designed for rapid national activation, with mobilization timelines measured in hours and days rather than weeks or months. 

Reserve formations are built to restore full-spectrum combat power quickly. 

After the Oct. 7 attack, Israel called up roughly 300,000 to 360,000 reservists, equivalent to approximately 3-4 percent of its population. 

Combined with its active-duty force, total personnel approached 5 percent at peak activation. 

This capacity reduces vulnerability in crisis but imposes immediate and concentrated economic and social strain.

This stands in stark contrast to the additive mobilization that has characterized the war in Ukraine. 

European defense planners are thus adjusting to a structural reality. 

Standing forces remain essential for deterrence and early phase operations, of course, but they are finite. 

Professional forces alone cannot guarantee long-term sustainability. 

Additive mobilization can expand manpower but risks accelerating functional decline if technical expertise is not preserved. 

The strategic reconsideration of reserves across advanced militaries evinces a recognition that modern war is a contest not only of firepower and maneuver but also of institutional resilience.

Still, European governments are not about to reinstate mass conscription. 

Reform efforts will instead focus on reserve readiness, recall flexibility and replacing lost expertise. 

Institutional adjustments – training throughput, administrative call-up mechanisms and integration between civilian employment and military service – can also be expected.

Differences will nonetheless emerge. 

Frontline states will prioritize rapid activation and territorial resilience, while larger economies will focus on preserving specialist capability within their reserve systems. 

These distinctions may appear marginal in peacetime, but they become decisive once sustained attrition tests the ability to regenerate lost capability.