“The concept is old. The application must be new.”
Nadia Schadlow, 10 June 2025
“We have completely eliminated the very idea of Russia having a strategic rear,” President Zelenskyy told NATO’s Summit Defence Industry Forum in Ankara this week. He went on to state that “for a long time, Russia believed it had a territorial advantage no one else possessed, a deep rear where it could safely keep military production, military equipment, and everything its war depends on, believing no one could reach them. We have reached them.”
While the long-range strike capability developed by Ukraine over the past four years is a stunning achievement, Zelenskyy’s speech prompts a deeper theoretical question. Are we now observing the decline, or even the collapse, of one of the oldest concepts in strategic thought: that a state’s homeland, its industrial base, its logistics, and its means of military regeneration can be placed beyond an adversary’s reach simply by putting distance between them?
Described in the strategic studies literature as strategic depth, for the past century it has been treated as an immutable fact of national defence strategy. Zelenskyy’s Ankara speech prompts us to question whether this is still the case.
In reviewing this issue, it would be a mistake to see this only as Russia’s problem. The technology Ukraine employs is not Ukrainian alone. The drones, the intelligence collected in depth, and the sophisticated planning needed to penetrate deep into an enemy heartland are all proliferating far faster than the capability, infrastructure, and political will required to counter them. The closing of the distance that once separated a rear area from a front line is not a Russian problem. It is fast becoming a challenge for every nation, from Europe to the Pacific.
The question Zelenskyy posed to Russia, is there anywhere left that is truly safe, is now a question every nation and defence ministry must ask itself.
What Is Strategic Depth?
In its narrowest sense, strategic depth describes the space between an adversary’s forces and the political, industrial, and demographic centres that a nation needs to protect to retain its sovereignty.
Strategic depth as a concept has its roots in the work of theorists such as Sun Tzu, Clausewitz, Jomini, Fuller and others. Aleksandr Svechin’s Strategy, written after his experience of the First World War and the Russian Civil War, argued for a strategy of attrition built on trading space for time, at least in the initial phase of a war, and warned against concentrating industry near vulnerable frontiers.
Colin Gray’s later synthesis of the geography-time-strategy relationship in Modern Strategy situates this Soviet experience within a broader tradition, treating depth as one of several geographic variables, alongside chokepoints, buffer states, and heartlands, that shape but do not fix a state’s strategic options. As Gray notes, the geographical dimension of strategy is ubiquitous and permanent, yet varied in its specific influence upon particular conflicts at particular times.
Barry Posen, in The Sources of Military Doctrine, treated geography and the depth available to a defender as one of the enduring constraints shaping whether states adopted offensive, defensive, or deterrent doctrines. John Mearsheimer’s study of conventional deterrence made a similar point from the attacker’s perspective: a state’s willingness to risk war depends heavily on whether it believes it can achieve a rapid victory before a defender can trade space for time.
Robert Peters and Christine Leah, writing for the Global Security Review, describe strategic depth in similarly operational terms, as the space within a territory that lets a defender halt an adversary’s attack, mount a counterattack, and end the fighting on acceptable terms. Daniel McCauley, in the Small Wars Journal piece discussed further below, pushes the definition further, describing strategic depth as the spatial, temporal, and cognitive distance that allows a nation or a commander to absorb shocks, mobilise, and adapt before decisive outcomes occur.
Depth, therefore, is not merely territory. It is time purchased with territory, time in which a defender can mobilise, manoeuvre, absorb the first blow, and counterattack on more favourable terms. These definitions trace a steady move away from a narrowly geographic starting point towards something closer to a general theory of resilience under attack.
Nadia Schadlow argues in a 2025 essay that strategic depth can no longer be measured in miles. She proposes that states think about depth across three additional aspects: technological terrain, meaning cyberspace, outer space, and the defence industrial base, where she points to China’s Volt Typhoon intrusion into American infrastructure as an adversary actively planting depth inside a rival’s own territory; alliances, or “defending forward,” in which backing frontline partners such as Ukraine, Taiwan, and Israel forces an aggressor to divert attention and resources outward rather than concentrating them at home; and a more diffuse ability to complicate and preoccupy an opponent so that it never has the bandwidth to concentrate against any single target.
Daniel McCauley’s Small Wars Journal essay reworks strategic depth through the classical canon, from Sun Tzu and Clausewitz through Jomini, Fuller, and Liddell Hart to Soviet deep-battle theory, and arrives at a single reframing: depth is decision time, not territory. He defines it as the spatial, temporal, and cognitive distance that lets a state or a commander absorb a shock and adapt before an adversary can force a decisive outcome, and sets out five strategic approaches for manufacturing it: forward deterrence, deny-and-survive, strategic breadth, hybrid approaches, and distributed resilience. He illustrates this with examples including the Baltic states, which are building deterrent and cyber depth through NATO’s forward presence and whole-of-society resilience despite having almost no geographic depth at all, and Israel, which he treats as manufacturing temporal depth through decades of fused human, signals, and cyber intelligence that converts early warning into mobilised readiness.
The literature, in other words, no longer treats strategic depth as something a map alone can measure. It is now understood as the combination of space, time, alliance structures, and institutional resilience that together determine how much punishment a state or a movement can absorb before its core is placed at risk.
The Dimensions of Strategic Depth
Manufacturing strategic depth, whether a nation is proximate to its threats or not, comprises many different elements. The first is layered defence: forward-deployed military forces and space-based systems for intelligence collection and early warning are one defensive response in this register, an attempt to rebuild through technology what geography no longer guarantees.
