Every age had its own kind of war, its own limiting conditions, and its own peculiar preconceptions,” the defense theorist Carl von Clausewitz wrote in the early nineteenth century. There is no doubt that Clausewitz was right. And yet it is surprisingly difficult to characterize war at any given moment in time; doing so becomes easier only with hindsight. Harder still is predicting what kind of war the future might bring. When war changes, the new shape it takes almost always comes as a surprise.
For most of the second half of the twentieth century, American strategic planners faced a fairly static challenge: a Cold War in which superpower conflict was kept on ice by nuclear deterrence, turning hot only in proxy fights that were costly but containable. The collapse of the Soviet Union brought that era to an end. In Washington during the 1990s, war became a matter of assembling coalitions to intervene in discrete conflicts when bad actors invaded their neighbors, stoked civil or ethnic violence, or massacred civilians.
After the shock of the 9/11 attacks in 2001, attention shifted to terrorist organizations, insurgents, and other nonstate groups. The resulting “war on terror” pushed thinking about state-on-state conflict onto the sidelines. War was a major feature of the post-9/11 period, of course. But it was a highly circumscribed phenomenon, often limited in scale and waged in remote locations against shadowy adversaries. For most of this century, the prospect of a major war among states was a lower priority for American military thinkers and planners, and whenever it took center stage, the context was usually a potential contest with China that would materialize only in the far-off future, if ever.
Then, in 2022, Russia launched a full-scale invasion of Ukraine. The result has been the largest land war in Europe since World War II. And although forces under Russian and Ukrainian command are the only troops fighting on the ground, the war has reshaped geopolitics by drawing in dozens of other countries. The United States and its NATO allies have offered unprecedented financial and materiel support to Ukraine; meanwhile, China, Iran, and North Korea have all assisted Russia in crucial ways. Less than two years after Russia’s invasion, Hamas carried out its brutal October 7 terrorist attack on Israel, provoking a highly lethal and destructive Israeli assault on Gaza. The conflict quickly widened into a complex regional affair, involving multiple states and a number of capable nonstate actors.
In both Ukraine and the Middle East, what has become clear is that the relatively narrow scope that defined war during the post-9/11 era has dramatically widened. An era of limited war has ended; an age of comprehensive conflict has begun. Indeed, what the world is witnessing today is akin to what theorists in the past have called “total war,” in which combatants draw on vast resources, mobilize their societies, prioritize warfare over all other state activities, attack a broad variety of targets, and reshape their economies and those of other countries. But owing to new technologies and the deep links of the globalized economy, today’s wars are not merely a repeat of older conflicts.
These developments should compel strategists and planners to rethink how fighting happens today and, crucially, how they should prepare for war going forward. Getting ready for the kind of war the United States would most likely face in the future might in fact help the country avoid such a war by strengthening its ability to deter its main rival. To deter an increasingly assertive China from taking steps that might lead to war with the United States, such as blockading or attacking Taiwan, Washington must convince Beijing that doing so wouldn’t be worth it and that China might not win the resulting war. But to make deterrence credible in an age of comprehensive conflict, the United States needs to show that it is prepared for a different kind of war—drawing on the lessons of today’s big wars to prevent an even bigger one tomorrow.
THE CONTINUUM OF CONFLICT
Just under a decade ago, there was a growing consensus among many experts about how conflict would reconfigure itself in the years ahead. It would be faster, waged through cooperation between people and intelligent machines, and heavily reliant on autonomous tools such as drones. Space and cyberspace would be increasingly important. Conventional conflict would involve a surge in “anti-access/area-denial” capabilities—tools and techniques that would limit the reach and maneuverability of militaries beyond their shores, particularly in the Indo-Pacific. Nuclear threats would persist, but they would prove limited compared with the existential perils of the past.
Some of these predictions have been borne out; others have been turned on their heads. Artificial intelligence has in fact further enabled the proliferation and utility of uncrewed systems both in the air and under the water. Drones have indeed transformed battlefields—and the need for counterdrone capabilities has skyrocketed. And the strategic importance of space, including the commercial space sector, has been made clear, most recently by Ukraine’s reliance on the Starlink satellite network for Internet connectivity.
On the other hand, Russian President Vladimir Putin has repeatedly made veiled threats to use his country’s nuclear weapons and has even stationed some of them in Belarus. Meanwhile, China’s historic modernization and diversification of its nuclear capabilities have ignited alarm over the possibility that a conventional conflict could escalate to the most extreme level. The expansion and improvement of China’s arsenal has also transformed and complicated the dynamics of nuclear deterrence, since what was historically a bipolar challenge between the United States and Russia is now tripolar.
What few, if any, defense theorists foresaw was the broadening of war that the past few years has witnessed, as the array of features that shape conflict expanded. What theorists call “the continuum of conflict” has changed. In an earlier era, one might have seen the terrorism and insurgency of Hamas, Hezbollah, and the Houthis as inhabiting the low end of the spectrum, the armies waging conventional warfare in Ukraine as residing in the middle, and the nuclear threats shaping Russia’s war and China’s growing arsenal as sitting at the high end. Today, however, there is no sense of mutual exclusivity; the continuum has returned but also collapsed. In Ukraine, “robot dogs” patrol the ground and autonomous drones launch missiles from the sky amid trench warfare that looks like World War I—all under the specter of nuclear weapons. In the Middle East, combatants have combined sophisticated air and missile defense systems with individual shooting attacks by armed men riding motorcycles. In the Indo-Pacific, Chinese and Philippine forces face off over a sole dilapidated ship while the skies and seas surrounding Taiwan get squeezed by threatening maneuvers from China’s air force and navy.
The emergence of sea-based struggles marks a major departure from the post-9/11 era, when conflict was largely oriented around ground threats. Back then, most maritime attacks were sea-to-ground, and most air attacks were air-to-ground. Today, however, the maritime domain has become a site of direct conflict. Ukraine, for example, has taken out more than 20 Russian ships in the Black Sea, and control of that critical waterway remains contested. Meanwhile, Houthi attacks have largely closed the Red Sea to commercial shipping. Safeguarding freedom of navigation has historically been a top mission of the U.S. Navy. But its inability to ensure the security of the Red Sea has called into question whether it would be able to fulfill that mission in an increasingly turbulent Indo-Pacific.
The plural character of conflict also underscores the risk of being lured by today’s weapon of choice, which might turn out to be a flash in the pan. Compared with the post-9/11 era, more countries now have greater access to capital and more R & D capacity, allowing them to respond more quickly and adeptly to new weapons and technologies by developing countermeasures. This exacerbates a familiar dynamic that the military scholar J. F. C. Fuller described as “the constant tactical factor”—the reality that “every improvement in weapons has eventually been met by a counter-improvement which has rendered the improvement obsolete.” For example, in 2022, defense experts hailed the efficacy of Ukraine’s precision-guided munitions as a game-changer in the war against Russia. But by late 2023, some of those weapons’ limitations had become clear when electronic jamming by the Russian military severely restricted their ability to find targets on the battlefield.
ALL IN
Another feature of the age of comprehensive conflict is a transformation in the demography of war: the cast of characters has become increasingly diverse. The post-9/11 wars demonstrated the outsize impact of terrorist groups, proxies, and militias. As those conflicts ground on, many policymakers wished they could go back to the traditional focus on state militaries—particularly given the enormous investments some states were making in their defenses. They should have been careful what they wished for: state militaries are back, but nonstate groups have hardly left the stage. The current security environment offers the misfortune of dealing with both.
In the Middle East, multiple state militaries are increasingly fighting or enmeshed with surprisingly influential nonstate actors. Consider the Houthis. Although in essence still a relatively small rebel movement, the Houthis are nevertheless responsible for the most intense set of sea engagements the U.S. Navy has faced since World War II, according to navy officials. With help from Iran, the Houthis are also punching above their weight in the air by manufacturing and deploying their own drones. Meanwhile, in Ukraine, Kyiv’s regular forces are fighting alongside cadres of international volunteers in numbers likely not seen since the Spanish Civil War. And to augment Russia’s traditional forces, the Kremlin has incorporated mercenaries from the Wagner paramilitary company and sent tens of thousands of convicts to war—a practice that Ukraine’s military recently started copying.
In this environment, the task of building partner forces becomes even more complex than during the post-9/11 wars. U.S. programs to build the Afghan and Iraqi militaries focused on countering terrorist and insurgent threats with the aim of enabling friendly regimes to exert sovereignty over their territories. To help build up Ukraine’s forces for their fight against another state military, however, the United States and its allies have had to relearn how to teach. The Pentagon has also had to build a new kind of coalition, convening more than 50 countries from across the world to coordinate materiel donations to Ukraine through the Ukraine Defense Contact Group—the most complex and most rapid effort ever undertaken to stand up a single country’s military.
Nearly a decade ago, I noted in these pages that although the United States had been building militaries in fragile states since World War II, its record was lackluster. That is no longer the case. The Pentagon’s new system has demonstrated that it can move so quickly that materiel support for Ukraine has at times been delivered within days. The system has surged in ways that many experts (including me) thought impossible. In particular, the technical aspect of equipping militaries has improved. For example, the U.S. Army’s use of artificial intelligence has made it much easier for Ukraine’s military to be able to see and understand the battlefield, and to make decisions and act accordingly. Lessons from the rapid delivery of assistance to Ukraine have also been applied to the Israel-Hamas war; within days of the October 7 attacks, U.S.-supplied air defense capabilities and munitions were in Israel to protect its skies and help it respond.
But even though Washington has now demonstrated that it can build a foreign military with alacrity, the question will always remain as to whether it should. The cost of transferring valuable equipment to a partner involves considerations of the U.S. military’s own readiness levels and combat credibility. Moreover, such assistance is not merely a technical effort but a political exercise, as well, and the system has occasionally slowed down as it wrestles with dilemmas regarding the full implications of U.S. security aid. For example, to avoid tripping Russia’s redlines, Washington has spent inordinate time debating where, when, and under what circumstances Ukraine should use U.S. military assistance. This puzzle is not new, but given the destructive abilities of the rivals that Washington is now facing or preparing to confront, the stakes of solving it correctly are much higher than during the post-9/11 era.
The role of defense industrial bases in rival countries has also shaped the new contours of war-making. In the dozens of countries supporting Ukraine, domestic defense industries have not been able to keep up with the demand. Meanwhile, Russia’s defense industrial base has been revived after speculations about its demise proved to be greatly exaggerated. Although China’s support to Russia appears to exclude lethal assistance, it has nevertheless involved Beijing’s providing Moscow with critical technologies. And both Iran and North Korea have supported their defense industries by selling munitions and other wares to Moscow. The United States is not the only power to have recognized the value (both on the battlefield and back home) of supplying partner forces and building up their capacities; its adversaries have, as well.
Understanding the new diversity of warfighters and the increased complexity of their relationships to one another will be crucial in any future conflict in the Indo-Pacific. Lessons from Ukraine have informed the Biden administration’s turbocharged effort to strengthen Taiwan, which received foreign military financing for the first time in 2023. More broadly, strategists should consider how future state-on-state warfare might be combined with insurgency. They should also think through how a panoply of actors on and off the battlefield, including nonstate groups and commercial entities, might support the primary antagonists.
And as in Ukraine, regional coalition building will be critical to any support Washington supplies to Taiwan in the face of Chinese aggression. Although the number of countries that support Taiwan’s military remains slim, Washington’s European allies seem increasingly willing to acknowledge Taipei’s outsize relevance for regional security and stability. Chinese support for Russia’s destabilizing war has disabused most European leaders of the false notion that Beijing values stability above all else. This evolution in European views was reflected by the “strategic concept” NATO released in 2022, which noted that China’s “coercive policies” challenge the alliance’s “interests, security and values.”
THE RETURN OF DETERRENCE
During the two decades of the post-9/11 era, the concept of deterrence was rarely invoked in Washington since the idea seemed largely irrelevant to conflicts against nonstate actors such as al Qaeda and the Islamic State (also known as ISIS). What a difference a few years make: today, almost every debate about U.S. foreign policy and national security boils down to the challenge of deterrence, which is one key to managing escalation—the task, although neither glamorous nor gratifying, that broadly shapes Washington’s policy in both Ukraine and the Middle East.
In this new environment, traditional approaches to deterrence have regained relevance. One is deterrence by denial—the act of making it difficult for an enemy to achieve its intended objective. Denial can quell escalation even if it fails to prevent an initial act of aggression. In the Middle East, Israel was unable to stop Iran’s first major conventional attack on Israeli territory earlier this year, but it largely denied Iran the benefits it hoped to gain. Israel’s military repulsed almost all of the hundreds of Iranian missiles and drones thanks to its sophisticated air and missile defense systems and the collaboration of the United States and countries across the Middle East and Europe. (Shoddy Iranian equipment also played a role.) The limited repercussions of the attack enabled Israel to wait nearly a week to respond and to do so in a more limited way than would have been likely had Iran’s operation been more successful.
Deterring and prevailing in conflict will mean gaining access to more bases in more places.
The win was costly, however. The United States and Israel may have spent around ten times more in responding to Iran’s attack than Iran did in launching it. Similarly, the Houthis have used relatively inexpensive and small-scale tools to attack ships in the Red Sea dozens of times, disrupting a major shipping route and imposing massive costs on the global economy. In response to the Houthis’ low-cost, high-impact attacks, U.S. Navy ships have frequently depleted their magazines without significantly reducing the threat. Accounting for the extended deployments the navy has undertaken in the Middle East for deterrence purposes, including confronting the Houthis by using munitions to counter their attacks and strike their assets in Yemen, rebuilding and recovering ship readiness after this fight with a small local militia amid broader regional hostilities will wind up costing the navy at least $1 billion over the next several years.
Another traditional means of deterrence that has resurfaced is punishment, which requires threatening an adversary with severe consequences if it takes certain actions. At a few key junctures, Putin’s saber rattling brought the potential for nuclear weapons use to its highest point since the Cold War. During one especially fraught period in October 2022, U.S. President Joe Biden and his team worried there was a 50 percent chance that Putin would employ his nuclear arsenal. In calls with their Russian counterparts, senior American leaders made stern and timely warnings of “catastrophic” consequences if Moscow made good on its threats. Those warnings worked, as did a broader effort to persuade key Asian and European countries, most notably China and India, to publicly and prospectively condemn any role for nuclear weapons in Ukraine. Tugging Putin down the escalation ladder required a baseline understanding of how he viewed threats, serious attention to the signals and noise being sent across the entire U.S. government, and active feedback loops to ensure those assessments were accurate—all paired with robust diplomatic engagements.
SIGNAL ACHIEVEMENT
The return of total war, with its many moving parts and elevated risks, has revived an understanding of how signaling works in a crisis. The Biden administration postponed a routine intercontinental ballistic missile test soon after Russia’s invasion of Ukraine to demonstrate how responsible nuclear powers act in times of potential escalation. This test could have inadvertently conveyed to Putin an inaccurate signal with respect to future U.S. policy at a sensitive time—particularly as his invasion of Ukraine was stumbling, scores of countries were coming together to support Kyiv, and Ukraine’s military was fighting doggedly. The United States wanted to ensure that Putin picked up the right signals about U.S. intentions and didn’t get distracted by the noise that a missile test might have introduced.
Signaling has also been crucial to preventing escalation in the Middle East. During three key moments—the immediate wake of Hamas’s October 7 attacks in 2023, Iran’s drone and missile attack on Israel in April, and the days following Israel’s assassination of Hamas leader Ismail Haniyeh in Tehran in July—a calibrated mix of deft diplomacy, surges in military assets, coalition building, and crystal-clear public messaging prevented a massive regional conflict. Just after the October 7 attacks, Biden sent a message to Iran’s supreme leader, Ayatollah Ali Khamenei, warning against attacking U.S. personnel in the region, and U.S. Secretary of Defense Lloyd Austin deployed two aircraft carriers plus additional aircraft to the Middle East to make clear that Iran should not escalate by directly entering the conflict. The presence of robust U.S. capabilities such as air defense was also critical to preventing further escalation after Iran’s large-scale attack on Israel in April. But without U.S. partnerships with countries across the Middle East and Europe, the limits of those capabilities would have become clear, since the efficacy of those capabilities benefited, to some extent, from the cooperation and participation of these countries. And following Haniyeh’s killing, U.S. Secretary of State Antony Blinken asked the Qatari prime minister and the Jordanian foreign minister, among other officials, to help dissuade Iran from responding. The Pentagon also further boosted the U.S. regional military presence, including by publicly announcing the deployment of a nuclear-powered submarine to the Middle East.
Of course, there are drawbacks to relying too heavily and for too long on military force in pursuit of deterrence. So far, surging U.S. military assets in the Middle East for deterrence purposes has been the right approach; through September, Hezbollah had largely kept its attacks on Israel below a certain threshold rather than overwhelmingly intervening in support of Hamas. But as time passes, the deterrent value of military buildups abates, and they grow susceptible to the sunk cost fallacy—that is, adversaries become accustomed to factoring in the threat such buildups pose rather than fearing them, and they learn how to plan around them. There are also costs to military readiness, which may create an opening for adversaries to question the credibility of threats because they know that Washington cannot indefinitely sustain a bulked-up presence. And there are opportunity costs to consider. The U.S. military must juggle multiple threats around the world while pacing itself for a long-term competition with China. Bolstering deterrence in the Middle East over the last year has been important, but it has inherently limited the time, attention, and resources Washington has devoted to Indo-Pacific security.
WITH A LITTLE HELP FROM MY FRIENDS
As the United States grapples with the challenges of deterrence on the battlefields of Europe and the Middle East, it is doing so with one eye on the Indo-Pacific, where China’s modernized military is undermining regional security. In the mounting U.S.-Chinese rivalry, the Pentagon’s approach will rely on another form of deterrence, which the 2022 U.S. National Defense Strategy dubbed “deterrence by resilience”—that is, “the ability to withstand, fight through, and recover quickly from disruption.” Resilience is the rationale behind the ongoing dispersal of U.S. military bases in the Indo-Pacific, which will allow American forces to absorb an attack and continue fighting. This effort has involved gaining access to four military bases in the Philippines; advancing new U.S. Marine and U.S. Army capabilities in Japan; forging several major initiatives with Australia, including increased submarine port visits and aircraft rotations, deep cooperation in outer space, and substantial U.S. and Australian investment in basing upgrades; and securing a defense cooperation agreement with Papua New Guinea that will allow for U.S. assistance in upgrading the country’s military, increasing its interoperability with the U.S. military, and performing more joint exercises. Meanwhile, over the last year and a half, a U.S. submarine with the ability to fire a nuclear-armed ballistic missile made a port call to South Korea, and an American B-52 bomber capable of deploying a nuclear weapon landed there.
The presence of increasingly capable U.S. military assets dispersed across the region (alongside those of allied and partner militaries) complicates Chinese planning. To some extent, this approach turns Thomas Schelling’s deterrence theory upside down. Schelling stressed the utility of certainty in signaling. What Washington is doing with its military in the Indo-Pacific, by contrast, creates several potential pathways to preclude Chinese efforts to overturn the status quo, increases the complexity of those contingencies, and induces uncertainty about which may be the most relevant. It’s true that it will be difficult to know whether any particular U.S. partner will prove willing to use or allow the use of military assets from its territory in a conflict. But that uncertainty is a feature, not a bug. Simply put, although the United States may not have full clarity about what role specific allies and partners will play should a conflict erupt, neither does China.
Adding further complexity to the picture is the way that in recent years, U.S. diplomacy has brought countries within the Indo-Pacific together and created connections between regions. The former is illustrated by the historic U.S.-brokered progress between Japan and South Korea, which has yielded more than 60 meetings and military engagements between them and the United States since 2023; the latter is represented by the creation of AUKUS, a major military partnership joining Australia, the United Kingdom, and the United States. Less formal but meaningful relationships have formed, as well. A grouping nicknamed “the Squad” is composed of Australia, Japan, the Philippines, and the United States; their defense ministers have met a few times, and their militaries ran maritime patrols in the South China Sea earlier this year. And nearly 30 countries in Asia, the Middle East, Europe, and the Western Hemisphere participated in RIMPAC 2024, a U.S.-led military exercise held in the Indo-Pacific.
Taken together, these campaigns demonstrate a modernized approach to collaborating with allies and partners in the service of deterrence. They are increasingly integrated by design and thus require a huge amount of work. The transformation of export control systems to enable the AUKUS partnership, for instance, took countless hours of collaboration among all three countries and involved scaling major bureaucratic hurdles even though the arrangement involved two long-standing U.S. allies.
Expanded partnerships of this sort can be unwieldy, and adversaries and competitors will do what they can to fracture them. U.S. partners may take ill-considered risks when facing rivals if they believe they hold an insurance policy in the form of American support. And deeper collaboration among Washington and its friends could be interpreted in a way that inadvertently escalates a competitor’s perceptions of insecurity. But overall, these tighter relationships are a net positive, and increasing the size, scope, and scale of collaboration makes the challenge tougher for those who seek to upend the security environment.
AVOIDING TOTAL WAR
Prevailing in an era of comprehensive conflict requires a sense of urgency and vigilance and, above all, a wide aperture. The circumscribed struggles of the post-9/11 era are gone, and today’s wars are increasingly whole-of-society phenomena. Focusing on boutique capabilities is shortsighted; both newer and older systems remain relevant. Participants on and off the battlefield proliferate, and parties increasingly collaborate. Actions and activities rarely affect just one domain; spillage seems unavoidable.
For Washington, understanding this new kind of total war will be essential to preparing for contingencies in the Indo-Pacific. The United States must continue expanding and diversifying its military posture in the region. Deterring and, if necessary, prevailing in conflict will mean gaining access to more bases in more places. Washington’s military support for Taiwan will be crucial. The United States must keep improving the speed at which it can deliver assistance to Taiwan and use more realistic conflict scenarios to inform what equipment it sends. This aid should continue alongside efforts to encourage meaningful personnel and organizational reform of Taiwan’s military, which would involve prioritizing and sufficiently resourcing training (including by preparing troops for more realistic scenarios) and further investing in asymmetric platforms and operational concepts.
Building on U.S. alliances and partnerships in the region will require serious and steadfast attention. Some relationships are ripe for revitalization. U.S. relations with India have moved slowly since the two countries announced a strategic partnership nearly 20 years ago. But clashes between China and India since 2020 have fundamentally reshaped the trajectory of New Delhi’s approach to Beijing; India now recognizes that this is a tense competition.
Today’s global security environment is the most complex since the end of the Cold War. Learning from wars that others wage can be difficult, but it is ultimately better than learning those lessons directly. The destruction and loss of life in Ukraine and the Middle East have been heartbreaking. In addition to helping its allies prevail in those conflicts and fostering peace, Washington should get ready to fight the kind of total war that has ripped apart those places—which is the best way to avoid one.