How much security is enough security? During the Cold War, the question was rather straightforward. The United States had one adversary — the Soviet Union — which it would need to deter and if necessary, defeat. For the last three decades, this deceptively simple question has proven exceedingly difficult to answer. For years, American defense strategy argued for a “two-war construct,” namely that United States should have sufficient military capability and capacity to fight and win two simultaneous wars in different theaters against major regional powers, like Iraq and North Korea. Over the last decade, though, as America’s military shrank in size and its adversaries grew increasingly capable, it backed off such aspirations.
Today, the prospect of America’s needing to confront a multi-front, multi-adversary set of conflicts has grown. By its own admission, the United States has a “pacing” challenge in China, an “acute threat” in Russia, and a host of lesser problems in the form of Iran, North Korea, and terrorism. Buying enough weapons and platforms to field a military to defeat all, or even two of these foes simultaneously, would likely be prohibitively expensive. By contrast, focusing only on one — to the exclusion of others — carries its own risks of encouraging an adversarial power to try and take advantage of perceived American weaknesses.
The Ukraine war has suggested a new “two-war” construct, one that may square this strategic circle while also allowing for the United States to guard against the possibility of multiple simultaneous crises without doubling the defense budget. Specifically, the United States should size its military to win one war against one major power but size its defense industrial base to provide the wherewithal to win two wars simultaneously — allowing the United States to fight one war directly and another by proxy.
The Rise and Fall of the Two War Force
The idea that Washington should be able to fight multiple wars in multiple theaters dates as far back as World War II when the United States and its allies fought Nazi Germany in Europe and Imperial Japan in the Pacific. During the Cold War, the United States codified the principle that it should be able to fight multiple wars at once into its defense strategy, although what that meant in practice was left open to interpretation. Successive administrations debated on what the appropriate combination of multiple major wars and smaller other “brushfire” conflicts should be to benchmark for the American military. As a result, the force-sizing conflict varied widely over the decades from a one-and-a-half-war construct (one major war in one theater and one brushfire conflict elsewhere) under the Nixon administration to two major wars and two brushfire conflicts under the Reagan administration.
When the Cold War ended, the United States needed a new benchmark for how much security to buy and what resources could be redirected away from defense and toward domestic priorities. Instead of a single peer adversary, the United States faced a series of lesser challenges from states like North Korea, Iran, and Iraq. While any one of these states could not match the American conventional military might, the United States could be repeatedly challenged to fight several conflicts simultaneously. And so, American defense strategies — like the Clinton-era Bottom Up Review —proposed that the United States military should be sized to tackle both the Persian Gulf and Korea scenarios at the same time.
For the next two decades, this two-war framework remained the essential building block of American strategy. While different Defense Department leaders tweaked the verbiage, the basic idea that the United States should be able to fight two wars at once remained constant.
By the early 2010s, however, calls for the “nation’s armed forces to be able to fight and win two major regional conflicts” were ringing increasingly hollow. For years, the United States has privileged capability over capacity in its force design. As result, the military shrank to a fraction of its Cold War strength by almost every measure: in personnel, aircraft, and vessels, for starters, even as it grappled with strains of near continuous employment beginning with the first Gulf War, the crises in the Balkans, and then the invasions of Afghanistan and Iraq. While the platforms may have become more advanced, even the most capable tank, ship, or aircraft can only be in one place at a time. As a result, fighting the Iraq and Afghanistan wars simultaneously nearly stretched the United States military to its breaking point. And those wars were both counterinsurgencies against terrorist groups — not high-end conventional conflicts against states with modern armies.
During the same period, America’s adversaries were growing more formidable. China was coming into its own as a military power, blunting the conventional U.S. military advantage in East Asia. After a decade of sharp decline following the collapse of the Soviet Union, Russia embarked on its own large-scale modernization effort, shedding its Soviet roots and adding new capabilities. North Korea developed nuclear weapons and a vast array of delivery vehicles to deter pre-emptive U.S. military action. While the United States was still the world’s dominant military, the idea that the United States could fight both adversaries at once was increasingly a herculean assumption.
And so the Department of Defense slowly backed off from its two-war force. The Obama, Trump, and now Biden administrations have all acknowledged that the United States faced multiple threats — specifically from China, Russia, Iran, North Korea, and terrorism. Each administration demurred, however, from stating that the U.S. military would ever need to fight two of these actors at the same time.
Instead, defense strategies talked of winning a war against one adversary at time while trying to hold the others in check. The Obama-era 2011 Defense Strategic Guidance talked of “defeating aggression by any potential adversary” while “impos[ing] unacceptable costs” on another. The Trump-era 2018 National Defense Strategy argued that the military should be able to be capable of “defeating aggression by a major power; [while] deterring opportunistic aggression elsewhere.” And the Biden-era 2022 National Defense Strategy similarly called for the need to “prevail in conflict” yet still “deter opportunistic aggression elsewhere.” The two-war force construct had yielded — both in deed and word — a one-war force, and noted defense analysts were writing a “eulogy” for the concept.
An Increasing Risky Bet
Underlying the shift to a one-war force was a big strategic bet — namely that U.S. adversaries are internally divided and therefore unlikely to launch wars simultaneously. For a time, the premise seemed reasonable. China and Russia, after all, fought a war against one another. China and Russia also joined the West in negotiating a deal to curb Iran’s nuclear program. North Korea and Iran are half a world apart. Even relations between China and North Korea have been strained at times.
Moreover, each of the adversaries appeared to operate on different timelines. Iran and North Korea seemed to be the most immediate threats, given the former’s ongoing proxy war activity and the latter’s regular missile and nuclear tests. While Russia — at least prior to February 2022 — and China posed longer term challenges. Even the most recent 2022 National Defense Strategy includes some of this sequential thinking: China is “the pacing challenge,” while Russia is merely an “acute” — or short term — one. And if threats only reared up sequentially, then the United States could reasonably assume that it would only need to tackle one adversary in one theater at a time.
But the geopolitical winds are changing. For starters, American adversaries are increasingly militarily intertwined. Russia has long been in the arms business — selling air defense systems to Iran and aircraft engines to China, among other items. Today, though, the relationships are more bidirectional. Iran gave drones and North Korea shipped artillery shells to Russia to support its war in Ukraine. China supplied Iranian proxies with drones. North Korea proliferated missile technology to Iran and potentially offered its nuclear know-how as well.
Military cooperation between American adversaries now goes beyond mere weapons sales. Iran and Russia supposedly colluded on the response to the Syrian civil war, coordinating their military activities in the country. More recently, Iran provided advisors to assist Russia in using its drones in Ukraine. In return, Tehran has reportedly asked Moscow for help quelling protests. As National Security Council Spokesperson John Kirby said recently, Russo-Iranian ties are deepening into a “full-fledged defense partnership.”
Meanwhile, China and Russia have said their friendship has “no limits.” While China only has offered tepid support for Russia in its war in Ukraine, Beijing still has an interest in deepening military ties with Moscow. In fact, Chinese leader Xi Jinping has — at least in some estimations — doubled down on his relationship with Russia. The two have conducted multiple joint bomber patrols and participated in military exercises with much fanfare.
And the timelines for each of these threats are accelerating. Iran now regularly engages in low-level military aggression, including missile attacks near American diplomatic facilities. North Korea has hit another record year of missile tests. Russia is fighting a war in Ukraine and has threatened nuclear war. And the timeline for a potential Chinese invasion of Taiwan may have accelerated. Consequently, it is no longer implausible that more than one threat would bubble up at once. Indeed, several seem to already be bubbling.
Looking ahead, then, the premise that the United States will only need to fight one adversary in one part of the of the world seems like a bad bet. The United States may not yet be confronting a true “axis of evil,” but American adversaries are becoming more tightly aligned, leaving the United States with a one-war force for an increasingly multi-war world.
Solving the Simultaneity Problem
In general terms, the United States seems to have four options to confront the prospect of two simultaneous conflicts. First, the United States could limit its ambitions and say that certain threats don’t matter. Indeed, some China hawks made precisely this argument for why the United States should not intervene in the run up to the Ukraine war. Any conflict with Russia, they claim, would distract from the main adversary: China.
As tempting as this strategic reductionism may be, it is also impractical. Leaving aside the moral equities at play, the United States is a global power with global interests that cannot simply be abandoned. Moreover, if American adversaries are becoming an increasingly unified bloc, then focusing on one is simply not viable, even if the United States adopts a realpolitik approach.
Alternatively, the United States could try to deter a second war, as the 2018 and 2022 National Defense Strategies propose. Deterrence, however, is a notoriously difficult concept. Ultimately, the difference between whether an action deters, provokes, or is simply ignored depends less on what the United States does and more on how a handful of dictators perceive these actions. Consequently, there are plenty of examples of American deterrence failing — be it with Iranian actions throughout the Middle East, China’s increasing incursions around Taiwan, or most spectacularly, Russia’s invasion of Ukraine. While deterring conflict is always preferable, the United States needs a viable plan B should deterrence fail.
A third option is for the United States to actually build a full-fledged, two-war force — which is what some defense hawks propose. This is, however, a hugely costly proposition. Over the last 70 years, the cost of the average servicemember has more than doubled and by some estimates is nearing $140,000 per active-duty servicemember. There are good reasons for this growth. Attracting and retaining the high-quality talent necessary to fight modern wars is expensive. And building a true two-war force would require a lot more people. The People’s Liberation Army is larger by some dimensions — like personnel and fleet — even as its platforms may not be as capable. If the United States tries to build a military large enough to blunt a Chinese invasion of Taiwan, plus another contingency, it would truly come at an eye-watering price.
Moreover, even if the United States could pay such a bill, it is not clear that such a cost would a priori serve America’s strategic interests in the long run. Long-term competition with China, after all, is not just a military race but a battle for global influence playing out over a variety of other domains — economic, diplomatic, technological. Given the financial constraints on the United States, such a massive military expansion may come at the expense of these other forms of power — or at the risk of America’s overall economic vitality.
But perhaps there is a fourth option: the Ukraine model. Sometimes lost in the debate over military aid to Ukraine is that the war — from a cold-hearted realpolitik perspective — has offered the United States a great return on its strategic investment. For roughly $20 billion so far, the United States has been able to help Ukrainian forces defend its territory and by so doing decimate the Russian military, its second-most militarily formidable adversary. Of course, the $20 billion does not reflect the full cost of the war for the United States: There is the humanitarian aid to Ukraine, the cost of the additional 20,000 troops the United States sent to Europe to bolster deterrence on NATO’s eastern flank, and further wear and tear on assets sent to defend NATO airspace. But even accounting for the total $100 billion that Congress has allocated to Ukraine, it is not a lot — at least, not in comparison to the overall American defense budget, which is set to approach nearly $860 billion next year. All in all, Ukraine provides a model for what a reasonably cost-effective way of fighting a second conflict might look like in the future.
Beyond the cost savings, though, the Ukraine model also offers strategic flexibility. With China, Russia, North Korea, and perhaps in the future Iran having nuclear arsenals, there are plenty of reasons why future American policymakers may want to avoid direct American military intervention. Indeed, even bracketing nuclear questions, large-scale conventional conflict would almost certainly be a bloody affair. Building the capability to fight indirectly at the very least provides another option.
Of course, the viability of such a strategy depends somewhat on finding future Ukraine-type scenarios — that is, countries with the leadership and national resolve to effectively employ such military aid. Other attempts to equip militaries and let them fight the wars have ended in calamity, most notably in Iraq and Afghanistan. And yet, there is reason to believe that the United States might have more Ukraines, and fewer Iraqs and Afghanistans, going forward. For starters, the United States presumably will not be trying to rebuild militaries from scratch anymore, like it did in Afghanistan and Iraq. Moreover, foreign invasions are also more likely to produce a rally-around-the-flag effect than internal conflicts as populations unite against a common enemy, as the Ukrainians did against the Russian onslaught.
In other words, the United States cannot always assume that it finds another Ukraine — a partner that is willing to fight and capable enough to do so successfully, if only given the right tools. Still, Ukraine may not be a unicorn, either. And as a means of balancing in a multi-threat but still fiscally constrained world, the Ukraine approach may be best available approach.
The New Two-War Construct and a Return to the Arsenal of Democracy
The United States will always need to be able to fight and win at least one major war on its own. Like any sovereign country, the United States has its own interests and needs to be able to protect them alone, if it must. It cannot always assume that it will have as motivated and as a capable of allies and partners as Ukraine as proven to be. And in some cases, especially when it comes to countries as formidable as China, the threat may be so great that any amount of military aid — absent direct American military involvement — might be insufficient.
Still, the Ukraine war offers a potential model of how the United States could deal two conflicts as once, especially if one of those conflicts is against one of America’s secondary adversaries — the Russias, Irans, and North Koreas of the world. Even if the United States is tied up with one conflict in one theater, then at the very least, the United States can offer its allies and partners the military wherewithal to win if they choose to fight. In this sense, the United States might not look at its support of Ukraine as a one-off response but rather as a potential model for future defense strategy — and as a way to hedge against the simultaneity problem.
Such a move would not be cost-free. Most notably, it would require a substantial expansion of the defense industrial base, which has been struggling to provide munitions for the Ukraine war. Whatever the cost may be, it would still be but a fraction of building out the force structure required to fight two wars at once and is considerably less risky than ignoring the problem altogether. In other words, it might offer a plausible way to keep American objectives and resources in line without sacrificing too much in either.
Over 80 years ago, Franklin Delano Roosevelt pledged that “[w]e must be the great arsenal of democracy.” Today, it could be time for the United States to renew that pledge — if not for the world’s sake, then perhaps for ours.
Raphael S. Cohen is a senior political scientist and the director of the Strategy and Doctrine Program at Project AIR FORCE at the nonprofit, nonpartisan RAND Corporation.
Image: U.S. Air Force photo by Airman 1st Class Cydney Lee
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