In 2017, we wrote a book arguing that the United States faced simultaneous tests from Russia, China, and Iran. We argued that these tests, or “probes,” were occurring at the outer perimeter of U.S. power—the “unquiet frontier,” as we called it. Front-line allies, such as Poland, Israel, and Taiwan, we wrote, were tempting targets for the United States’ adversaries because of their vulnerable geography and great distance from the U.S. homeland.
Seven years later, this frontier is more than unquiet—it is in flames. On the European frontier, the largest war since 1945 is entering its third year. On the Middle Eastern frontier, Iran is using its network of proxies to wage an undeclared war against the United States and Israel. On the Asia-Pacific frontier, China is accumulating military assets to cross the Taiwan Strait.
Collectively, these moves suggest that the United States’ rivals are not only probing the firmness of the frontier adjacent to them but also anticipating a dramatic opportunity to upset the wider order that has underwritten Western security and well-being for decades. The frontier—and with it, the entire game board—is in crisis.
All of this may be sobering to a generation in the West expecting the world to become an ever-expanding zone of peace. But there’s nothing new about it. Historically, the strength of a great power and the political order it embodies have been shaped by events on the frontier more than events in the relatively safer confines of the imperial interior. Rome’s great crises began on the banks of the Rhine, Danube, and Tigris. The British Empire’s moments of truth were in Natal, the Hindu Kush, and the Sudetenland.
Then, as now, moments of violent upheaval naturally prompt debates about the character of geopolitical change and the right strategies to cope with it. How should a great power manage a lengthy and distant frontier under attack? While the United States is unique in the sheer scale of military and economic power it possesses, the question is no easier than it was for past empires; U.S. power, like theirs, has limits. It is limited in quantity, by geographic distance, by domestic concerns, and by Americans’ own, often fickle political will. The United States’ predicament, in other words, is not new.
While the debate rages about how to handle what’s happening in Eastern Europe, the Middle East, and East Asia, it may be worth pausing to consider the situation from a historical perspective. Short of abandoning the frontier outposts under pressure from predatory powers, great powers in the past tended to follow five basic principles for managing an unquiet frontier.
First, the frontier is a violent place where war is always possible. By definition, the frontier is a zone of competition among rivals. It is an object coveted in its own right for its strategic location, but it is also the place where colliding agendas—between powers seeking to maintain the geopolitical status quo and those seeking to revise it—inevitably play out. While it is possible to mitigate the clash through negotiations, trade, or bribes, a frontier separates powers that have deep conflicts of interests grounded in history, civilizational contrasts, or ideological differences. As a result, violence is never too far below the surface.
This may sound obvious, but it’s worth stating upfront because it runs counter to a Western conceit that lasted until the very eve of Russia’s full-scale invasion of Ukraine: namely, that old-fashioned wars of conquest don’t happen nowadays, even in historically fraught locations, because of the civilizing effects of liberal institutions or globalization—or the deterrent effect of all-powerful military technology. That’s not true and probably won’t ever be true. Violence is endemic to the frontier, and the current wars and threats in Ukraine, the Middle East, and East Asia should have surprised no one. A realistic strategy to manage violence along the frontier begins by recognizing that fact, as well as its corollary: that preserving the status quo requires an unsleeping vigilance in these distant places. No international institutions or sets of rules will prevent the United States’ rivals from seeking to expand their control over key regions in Eurasia, where Washington has vital economic and political partners.
Second, well-armed and motivated frontier states are the best deterrent on the frontier. What the inhabitants of the frontier have in common with the distant power is a desire to not see the frontier fall into the hands of a nearby bully. The distant power’s motivation is to prevent the rival from accumulating a bigger power base. But the frontier state’s motivation is much, much greater and more personal: ensuring its own survival. It has the most to lose if the frontier breaks and disgorges Scythian hordes.
This greater motivation makes frontier states the most effective source of resistance to threats against the frontier. They are the first responders, and their determination is the foundational bloc of a stable frontier. Local resolve trumps United Nations resolutions. From the standpoint of their great-power patron, it is also a very good thing to work with the momentum of locals’ desire to resist—whether it takes the form of Ukraine’s struggle to not be absorbed into a new Russian empire, Israeli defiance of Iranian plans for regional dominance, or Taiwan’s effort not to be subsumed under the Chinese Communist Party’s rule. Countries at the frontier are a source of amply motivated, effective, and legitimate resistance to their own enemies; without that resistance, the superpower patron would have to venture much more of its own blood and treasure. There may, of course, be many differences between the front-line state and its far-away patron, but at least on this core strategic point—that the frontier should not be breached—their interests naturally converge.
Third, preclusive defense is the preferred strategy. Preclusive defense actively guards a frontier by positioning sufficient forces to repulse an initial attack and conduct local counteroffensives. Treating a frontier as a flexible line, with the option of pulling back when under pressure, is tempting, especially when military resources are scarce or unavailable. But the cost of sacrificing space for time—defense in depth—is much higher than it may appear because front-line allies will peel away. If the ally thinks it is expendable—that its territory and people are the space to be given to the enemy in a tactic to gain time to arrest the attack elsewhere—that ally will lose the resolve to defend the frontier. Alone, with no outside help, the choice for a frontier state becomes one between accepting a change in the status quo and resisting at high cost with a low probability of success. Some, such as Ukraine, may choose the latter, but it is not a given that this is the most common path. In fact, the heavy costs incurred by Ukraine may plausibly dissuade others, such as Taiwan, from following its example. When a front-line ally wobbles and falls under the rival’s control, the distant patron loses its ability to shape the regional dynamics. This is especially dangerous when the patron is a maritime power that has no depth to give: Such a power either keeps a port or thin littoral or is fully expelled from the region with no chance of a cost-free return.
The value of frontier allies is that they create the potential for striking beyond the frontier line, on the territory of the predator state itself. The very potential for such attacks strengthens deterrence because the frontier state’s strong motivation for self-defense lends credibility to its threats. That requires it to be capable of inflicting heavy costs on—or launching punitive raids against—the nearby predator state. Thus, paradoxically, the stability of a frontier is helped by the local ability to escalate. Such escalation is kept in check by the fact that the front-line state is the first to bear the brunt of the rival’s response, establishing powerful incentives to strike only as required for the operational purpose of keeping the frontier stable. In other words, a small frontier state, even if well armed, is unlikely to ever march on the capital of the rival.
Ukraine’s ability to strike Russian military targets deep in occupied Crimea or immediately beyond the border would weaken Russia’s offensive actions—and if a cease-fire ever occurs, this continued ability would reinforce deterrence. Similarly, Taiwan could more effectively deter China if it had the capability and clear will to strike not just the immediately attacking forces but also Chinese ports. In brief, deterrence is much stronger when the defender is not just holding the fortress but has the ability to strike an attacker’s encampments. Giving weapons, even very powerful ones, to the frontier state is a good investment.
Fourth, the reputation acquired or lost on one frontier matters on another. Predator states watch how their rival great power handles other, often distant frontiers to gauge the level of its power and the competence of its leadership. Reputation is particularly important for a maritime power, whose core challenge is the length of the frontier it has to manage combined with its distance from the homeland. Given naturally finite means, it is difficult to maintain substantial and perpetual presence in any and all directions. Strategic ubiquity is an illusion, a calculated bluff predicated on reputation.
What follows from this is that it pays to stop aggression at the frontier early when and where it happens first. How the initial fires are dealt with will have a big bearing on whether they spread into a wider system crisis. Ignoring the early ones in hopes of keeping powder dry for later ones is dangerous, and the best strategy is to decisively sequence the frontiers. Today, that means using Russian President Vladimir Putin’s attack as an opportunity to impose a strategic defeat on Russia, the weaker of the United States’ two main rivals, before the stronger of the two, China, is ready to move against Taiwan. Washington should not attempt to shift priorities midstream.
Fifth, once breached or abandoned, a frontier is costly to stabilize. As defense is cheaper than offense, so is maintaining a frontier versus restoring the status quo ante. In the most dramatic case, when the great power is pushed out from (or leaves) a front-line region, reentry is extremely difficult both for military and political reasons. Militarily, trenches and fortifications—and in today’s high-tech environment, an array of anti-access and area denial weapons—impose high casualties on the attacking side. Politically, abandoned front-line locals will likely make different calculations: Facing their nearby enemies as their security patron leaves, they may decide that their least bad choice is to cozy up to their enemies. Reentry for the great power that has left becomes thus a costly and solitary effort with limited indigenous support. If the United States abandons Ukraine, Israel, or Taiwan today and these places fall under a rival’s sphere of influence, it is unlikely that this could be reversed in our lifetimes without a much steeper cost in blood and treasure than if Washington had simply helped them to defend themselves adequately in the first place.
In all of these cases, the point is that bolstering the frontier is not an act of charity for a great power like the United States today. Instead, it is an act of enlightened self-interest that, if undertaken with energy and forethought, offers a cost-effective way of securing the homeland itself. The United States has a long tradition of thinking in very practical terms about unquiet frontiers, on both its own continent and the Eurasian rimlands. These were and are the regions where the noble and pacifying tools of institutions and laws, the calculations of merchants, and the impartiality of judges have a tenuous effect. Ultimately, how these frontiers are ordered is the product of a firm hold exercised through violence or threat thereof. That reality has not changed, and the wars in Ukraine and the Middle East are testaments to the frontier’s eternally ferocious nature.
In the current situation, history suggests that the United States’ best bet is to prevent its rivals’ probes on the frontier from becoming a wider, systemwide run on the bank. Whether the first probe succeeds or fails matters disproportionately for determining whether a sequence of probes occurs. While Asia matters most for the United States strategically, defeating ongoing aggression on the European and Middle Eastern frontiers—if that can still be done—remains the optimal strategy. The best way to do that is to provide weapons to Ukraine and Israel, including weapons that Washington might not normally be comfortable dispersing. Doing that, in turn, will require a serious effort to strengthen the U.S. defense industrial base, which will be needed in the long confrontation with China as well.
What the United States does on these distant frontiers is, of course, of secondary importance if the more immediate frontier—the national border—is broken. When we wrote The Unquiet Frontier, we did not expect that the U.S. southern border would become so unstable, not to mention becoming so at the same time as geopolitical rivals amp up the level of violence in Eurasia. Fixing the border is thus not just a domestic priority but a foreign-policy prerequisite: The distant frontier will be abandoned sooner or later if the national border becomes a locus of instability.
It is not too late. Even though U.S. rivals have improved their position in recent years, advancing their control and building up their arm stores, Americans still have an opportunity to conserve a modicum of international order and security. It’s better to stop predator states at the far frontier by backing the efforts of motivated locals than attempting to do so after these places are lost. And it’s easier to keep things stable than to bring back stability after it’s lost. And that begins, and ends, at the frontier.