THE GREATEST risk facing the twenty-first-century United States, short of an outright nuclear attack, is a two-front war involving its strongest military rivals, China and Russia. Such a conflict would entail a scale of national effort and risk unseen in generations, effectively pitting America against the resources of nearly half of the Eurasian landmass. It would stretch and likely exceed the current capabilities of the U.S. military, requiring great sacrifices of the American people with far-reaching consequences for U.S. influence, alliances, and prosperity. Should it escalate into a nuclear confrontation, it could possibly even imperil the country’s very existence. 

Given these high stakes, avoiding a two-front war with China and Russia must rank among the foremost objectives of contemporary U.S. grand strategy. Yet the United States has been slow to comprehend this danger, let alone the implications it holds for U.S. policy. So far, Washington’s efforts to grapple with the “simultaneity” problem (as it’s called in Pentagon circles) have been overwhelmingly focused on the military side of the problem. The 2018 National Defense Strategy (NDS) replaced the two-war standard with a laser focus on fighting one major war with America’s most capable adversary—China. In its wake, a debate has erupted among defense intellectuals about how to handle a second-front contingency. 

By comparison, there has been much less discussion of how, if at all, U.S. diplomacy should evolve to avert two-front war and, more broadly, alleviate the pressures of strategic simultaneity. While the Trump administration rightly inaugurated a more confrontational approach toward China, this was not accompanied by a rebalancing of diplomatic priorities and resources in other regions to complement the NDS’ justified focus on the Indo-Pacific. Nor does the Biden administration appear to be contemplating a redistribution of strategic focus and resources among regions. This misalignment in the objects of U.S. military and diplomatic power is neither desirable nor sustainable. America will have to limit the number of active rivalries requiring major U.S. military attention, improve the functionality of its existing alliances for offsetting the pressures of simultaneity, or significantly grow defense budgets—or some combination of the three. 

In the current budgetary environment, though, the most likely outcome could well be the worst of all worlds—namely, that America will continue to try to overawe all threats without significantly improving the performance of its alliances while reducing real defense spending. Such an approach keeps U.S. power thinly spread and limits Washington’s bandwidth for managing policy tradeoffs among regions. This creates an ideal setting for an increasingly aligned Russia and China to conduct repeated stress tests of U.S. resolve in their respective neighborhoods and, when conditions are ripe, make synchronous grabs for, say, Taiwan and a Baltic state. 

Averting such scenarios should not only or primarily be a concern for the U.S. military; it is also the job of U.S. diplomacy. Indeed, diplomacy in its highest form has historically been used for precisely this purpose, as an instrument for rearranging power in space and time to avoid fighting numerous enemies at once. This role—the sequencing of rivalries—should be the central preoccupation of American diplomacy today. Rather than trying to contain Russia and China simultaneously, the United States needs to find a way to stagger its contests with these two powers to ensure that it does not face both at the same time in a war. 

While accomplishing this task will not be easy, COVID-19 may present an unexpected opportunity. By widening the power disparity between China and Russia, the pandemic has heightened Russia’s economic dependency on China as a source of capital, markets, and international political support. Paradoxically, the very fact of this deepening dependency is likely to increase Russian fear of becoming a sidecar to Beijing’s ambitions and create incentives for Moscow to reorient its foreign policy. 

Within this paradox lies an opportunity for the United States. The aim of American diplomacy—and the crux of our strategy for avoiding a two-front war—should be to sharpen Russia’s dilemma and render that country less menacing to ourselves on a faster timeline than China is able to realize its ambitious military potential as a great power. Rather than attempting to woo or court Russia into a conciliatory stance, we should present it with a combination of insuperable obstacles to westward expansion (including, if necessary, by inflicting a far more serious defeat than it has heretofore experienced in Ukraine) while presenting new opportunities for cooperation, investment, and growth in Russia’s east. Simply put, the goal should be to alleviate America’s simultaneity problem by giving Russia incentives to be less of a European power—and more of an Asian one. 

COMPETITION WITH more than one hostile peer in peacetime is not something that the United States has much experience navigating. The ability to outproduce, outgun, and outdistance multiple enemies, courtesy of America’s size, resources, and geography, was the key to U.S. success against all of its twentieth-century major power opponents. 

Freedom from two-front pressures reached its apogee after the Cold War, when the United States found itself in a strategic environment devoid of any peer competitor. This nimiety of power was reflected in the Pentagon’s maintenance, from the early 1990s onward, of the so-called “two-war standard”—under which it planned for wars against regional powers in the Middle East and Asia simultaneously. In such a setting, there was little need to contemplate significant tradeoffs between the country’s major objectives. Because America could be militarily strong in Europe, Asia, and the Middle East at the same time, there was no need for it to develop positional diplomacy to support shifts of concentration between these regions. 

By contrast with these greenhouse conditions, the defining characteristic of the emerging international landscape is the array of constraints that it presents to the exercise of American power. The rise of China confronts the United States with arguably the most capable adversary it has faced in its history as a global power. Most projections show China having, by 2030, an economy that will be between 1.5 and 2 times the size of America’s and a population more than four times as large. By 2049, Beijing has the stated intention of possessing a military that outclasses America’s. By some estimates, it has already reached parity in important categories of military power. 

China’s rise is accompanied by other unfavorable permutations in the international system. Chief among these is Russia’s persistence as a militarily capable and politically motivated opponent. Russia’s significance is often downplayed because of its relative demographic and economic weakness. But Russia remains a great power by virtue of its physical size, population, and possession of one of the world’s two largest nuclear arsenals. Russia’s leaders, more than those of any other large power, identify their country’s interests in terms that are antagonistic to the United States. Indeed, as a growing list of hostile Russian actions demonstrate, Moscow is already waging a kind of war on America. 

From a U.S. strategic perspective, it is the confluence of threats from these two large powers that presents the organizing challenge for the United States. The proposition here is not that the two will necessarily form a durable military alliance—though that is certainly possible. Rather, it is that these two large Eurasian states function in ways that tend to amplify threats from the other. 

This takes the form, first, of synchrony, or action by both powers that threatens U.S. vital interests in different regions simultaneously. As the recent build-up of Russian forces in Ukraine and Chinese ships off the Spratlys showed, the physical location of large adversaries at opposite ends of Eurasia would make it difficult for the United States to draw upon the same military capabilities for responding to both adversaries. 

Secondly, there is the distraction effect, whereby the actions of one of these states, even if uncoordinated, generate opportunities for the other that otherwise might not have existed. A move by Russia in the Baltics would create a favorable opening for China to move against Taiwan. This translates into a de facto second-mover advantage that would be very tempting for Beijing to exploit. And vice versa. Put differently, the very presence of a risk-acceptant Russia could catalyze a more aggressive China than might otherwise have been the case. 

IT WOULD be easiest if the United States could be able to handle the two-front challenge either entirely or primarily by military means by simply adopting a supersized version of the two-war standard that it maintained after the Cold War. If this were possible, we would not need to worry overly much about developing diplomatic options to handle simultaneity because there would be no power gaps to address. We could safely assume the continued ability to deter, and if necessary, defeat, both powers at the same time. 

But that is not the case. Under plausible levels of defense spending, the Pentagon can reasonably plan to defeat one major opponent in a future conflict. That reality is a byproduct of both of America’s projected resources for defense, which are declining in real terms as a result of political priorities in the federal budget, and the capabilities being fielded by our two top adversaries. Indeed, even if the United States increased its defense budget, it would not be able to simply overcome this problem, given the growth in Chinese military spending in particular.