There are two basic ways to defend a frontier. One is through defense-in-depth: leaving the borderlands more or less undefended while concentrating military strength in the interior. This strategy accepts the cost of an enemy grabbing territory in exchange for time to mount a concerted counter-offensive in a place and moment of the defender’s choosing. Militarily, it works well against high-intensity threats (big armies) that the defender could never hope to repulse by spreading its forces across a lengthy periphery. It is also predicated on having the geographic depth necessary to allow a temporary retreat, followed by a regrouping and a counteroffensive. To trade space for time the defending state needs the former. Politically, it functions best in the hands of a unified polity that has clear, centralized control over its armies and can maneuver them to retreat and to counterattack. Because it accepts the danger of losing territory upfront, it relies on creating the certain knowledge in the mind of the enemy that, even if it takes a bit at first, the counterattack will be swift, certain and overwhelming.
A second strategy is defense by preclusion: actively guarding a frontier by positioning sufficient forces in-theater to repulse an attack and conduct local counter-offensives. Preclusion is the antithesis of defense-in-depth; where the latter virtually guarantees that battle will occur on home territory, the aim of the former is to keep the fight on territory other than the defender’s. Militarily, it uses forward-stationed forces to hinder the enemy’s advance. But it also seeks to create a zone of uncertainty and even instability beyond enemy’s lines that absorbs the energy of the opponent. It is a combination of border defense and offensive actions, rejecting the possibility of a space-for-time trade-off. Politically, preclusive defense is well-suited to divided polities or alliances where decentralized control over the military would make it difficult to quickly deploy armies from the center to recapture lost ground. It also assumes that the political unity needed to repulse a hostile attack will not necessarily materialize with the passing of time, and in fact may even be less likely. Unlike defense-in-depth, preclusive defense assumes that the defender will rarely have the luxury of time to bring reinforcements into play in the critical early phases of an attack. It acknowledges that, once lost, it may never be able to regain the territory.
These two broad concepts of frontier defense apply to individual states and alliances alike. NATO strategy today is implicitly based on the first concept, defense-in-depth. An unspoken truth in the Alliance is that NATO’s unevenly distributed force structures and fractious politics virtually guarantee that it would lose territory if attacked. Frontline NATO states are too small to defend themselves for long against an attack, and the Alliance refuses to maintain large forces on their territory. Thus in the event of an enemy’s assault, the Alliance would inevitably have to trade space for time, as weak Central European forces succumbed to a stronger opponent while larger Western states use complicated diplomatic mechanisms to generate political unity and organize a military response. In the best of scenarios involving a clear-cut attack, strong Allied leadership and quick political consensus, this could take several days. But against a Russian limited-war incursion like that used in Crimea, NATO’s defense-in-depth strategy could take weeks to come into play because the initial impulse to mobilize an alliance-wide response would be tempered by the end of the hostile advance. In a worst-case scenario, a military response might never come at all, as Alliance members bickered over whether the ambiguous nature of the incursion represented a real attack warranting Article 5.
Using defense-in-depth in today’s NATO creates two serious problems, one military and one political. First, it means a loss of deterrence. Russia knows that the Alliance is politically divided and is likely to be slow in response as long as the Russian incursion is sufficiently ambiguous in nature. This means that NATO’s conventional military strength—far larger than Russia’s—is unlikely to deter a Russian attack, since it is far away from the frontline and may never be actually used. And since most local CEE militaries are too weak to make a difference on their own (Poland is increasingly an exception), this places the full weight of deterrence squarely on the shoulders of the U.S. nuclear arsenal. But territorial defense cannot be maintained by strategic deterrence, since it would involve the use of the ultimate in destructive capabilities to prevent “little green men” from grabbing a few square kilometers of Lithuanian territory. The Russians don’t believe the Alliance would go to this length. With the Ukraine war as a dress rehearsal, they have essentially called the bluff of defense-in-depth.
The second problem with defense-in-depth in the era of limited war is that it is no longer possible to provide reassurance to frontline allies within the context of such a strategy. A resurgent imperialist Russia combined with NATO’s defense-in-depth posture threatens to turn Central Europe into a geopolitical speed bump, a space to sacrifice in order to slow down and negotiate a westward Russian advance. The example of eastern Ukraine’s de facto amputation has vividly demonstrated to frontline NATO states the costs of attempting to trade space for time in a military contest with Vladimir Putin. Out of weakness or incompetence, the Ukrainian military waged a defense-in-depth strategy and rather than buying time for a counter-offensive, it bought time for Putin to consolidate his gains and make them irreversible. Defense-in-depth works if the enemy wants to conquer the entire state, not if its objectives are satisfied by a limited territorial adjustment. For vulnerable CEE states like Poland, Estonia or Romania, the lesson was clear: if you are attacked, you cannot assume that the West’s reinforcements will reach you in time to reverse whatever new territorial fait accompli the Russians are trying to create. The takeaway for these states is, as Napoleon said, “rely only on your own arms.” To some like Poland, this means building a stronger modern military armed, if necessary with offensive weapons. But for some states lacking the culture of resistance, it could mean jettisoning resistance in favor of cooperative arrangements with Russia.
Few of NATO’s efforts in the nine months since the Ukraine crisis began have so far managed to plug the holes in defense-in-depth. Virtually all of the Alliance’s traditional fixes to CEE vulnerability—small trip wires, contingency planning, rapid response forces—all operate within the paradigm of defense-in-depth. They assume that an initial attack will succeed and seek to either trigger or speed up the arrival of reinforcements. The new response force created at the Wales Summit, for all the political ballyhoo, is still at heart a promise of future help by nations who may or may not agree on its use when the bullets start to fly. Even the prospect of U.S. tripwires (most of them temporary deployments of forces and assets to Central Europe), while valuable, does little to address the deeper problem, since the small American military presence can be bypassed using limited war methods. These forces are ultimately meant to make the prospect of Western reinforcements more politically credible, not stop the conceivable Russian incursion.
NATO will not be able to deter Russia or achieve lasting stability on its Eastern flank as long as it persists with a defense-in-depth strategy. This is a harsh reality that may be difficult to swallow politically but is strategically undeniable. To cope successfully with sharpened security dilemmas created by the war in Ukraine, the West needs to adopt a strategy of preclusive defense. Such a strategy would involve doing three things that are taboo in modern NATO circles.
The first is to increase the ability of frontline NATO states to take war onto Russian or neighboring territory. The congenital flaw of defense-in-depth in a limited war environment is the presumed indefensibility of the eastern quarter of the alliance—that vulnerable space that would be traded for time in a crisis. The quickest way to plug this gap is to make frontier NATO states indigenously capable of inflicting pain on an aggressor. A preclusive strategy for NATO would be anchored on the two largest and most capable military actors, Poland and Romania. These states occupy the northern and southern corners of the Baltic-to-Black isthmus and, uniquely among CEE states, possess the latent national potential to radiate stability in their respective sub-regions. The United States should ease and even subsidize the export of advanced offensive armaments to these states with a view to forming beefed-up “salients” that jut into those territories of the post-Soviet space upon which Russia would rely for assaulting NATO’s flank.
The fear that blocks us from doing so is that such capabilities are deemed destabilizing because they may create a “cult of the offensive.” But such fear is overblown. It is highly unlikely that states such as Poland, Romania or the Baltics would seek to attack Russia first; it would be suicidal. The only, however distant, possibility is that these countries could initiate a war out of desperation were they to be abandoned by the Alliance and the United States in particular. The U.S. continues to be an assuager of regional tensions. Far from destabilizing, giving offensive capabilities to local frontier allies enhances deterrence by increasing the credibility of the alliance. The immediate targets of a Russian limited war are in fact very credible users of such weapons, much more than their distant security protectors. Waiting for the enemy to come ten or even 100 miles into NATO territory before reacting will not prevent war because the response of the Alliance loses credibility. In fact, the longer the response time, the less credible it is.
Second, those portions of NATO’s outer “hide” that are less likely to be able to generate sufficient power to repel a Russian attack should be made unappetizing. While the Baltic States may be indefensible, that doesn’t mean they can’t be indigestible. One irony of Putin’s limited war techniques is that it levels the military playing field between Russia and small nations; even tiny frontline armies can be effective in denying columns of little green men the ease of access and movement needed to create territorial faits accomplis. Moreover, modern technology bestows great power on the defender with a whole spectrum of weapons that can increase the enemy’s costs of operating in the targeted country. Anti-tank weapons, precision-guided rockets, mines, and so on can bleed the aggressor’s forces, inflicting unexpected and unpalatable costs.
In a nutshell, the first set of capabilities hinders the ability of the revisionist to achieve a low-cost quick fait accompli; the second aims to make that fait accompli difficult to hold. Not only does the development of such capabilities strengthen the defense of the frontier, it also makes extended deterrence more likely to succeed. The ability of the frontier ally to be the first responder to a local foray by the revisionist power limits the clash to a border conflict, thereby increasing the willingness of the distant security guarantor to support the ally in such a localized confrontation and to back him in case it escalates to a larger conflagration. Or to put it another way, local defenses provide time and limit the conflict in such a way as to enable the intervention of security guarantors – the other NATO members and the United States in particular.
The third feature of a preclusive defense is perhaps the most difficult to accept and pursue. In order to increase the chances of success of such a type of defense, it is necessary to engage in full-spectrum competition beyond NATO borders to threaten the stability of the attacker on ground closer to his strategic center of gravity. This is at the same time more and less than kinetic attacks against the staging areas or logistical links in enemy territory. It is more because it engages the enemy along a wider spectrum of competition, including proxy wars that involve the cooptation of local forces and elites to create instability within the sphere of influence (in this case, the post-Soviet space) or on the border of the rival. It is less because it does not require direct military intervention of NATO forces and in many cases it may be limited to stirring political opposition in areas and territories under the rival’s control. The broad purpose is to create sufficient problems for the opponent to distract him from the potential attack, or to inflict costs if the attack were to materialize, while at the same time limiting NATO’s own direct involvement. The current war in Ukraine therefore represents an opportunity to show Moscow that the Atlantic Alliance is willing and capable of competing with Russia outside of its own borders.
Russia targets Western weaknesses, which are not material or economic. The West is by far superior to Russia in those areas. But Western security is based on an unjustified faith in defense-in-depth that, by sacrificing the easternmost allies to buy time to shore up a unified political will and regroup allied military forces, is not suited for the times. Russia is banking on its ability to accomplish quick, low-cost, low-intensity, territorially limited facts on the ground before a concerted NATO response is organized. Russia is not outmatching the West; it is outwitting it. To oppose Moscow on winnable terms will require us to break some taboos (arming the most exposed allies with both defensive and offensive capabilities, considering political and military competition outside of NATO borders). To win in the age of limited war, the West must adopt the methods and mentality of preclusive defense.