DOES THE United States benefit from having allies? In recent months, Donald Trump, the presumptive Republican presidential nominee, has voiced skepticism about the value of core American allies in Europe and East Asia. Trump argues that U.S. allies are free riding off the United States, and that their contributions to U.S. security are no longer sufficient to justify either the risks or the costs they impose on Americans. He is far from alone this election season. Surrogates for Bernie Sanders like Jeffrey Sachs have made similar arguments. Even President Obama himself expressed frustration about allies and partners that do not pull their weight in his recent Atlantic interview, as did former secretary of defense Robert Gates in his second memoir. In earlier years, politicians as diverse as President Dwight Eisenhower and the Democratic Senate majority leader Mike Mansfield issued similar complaints.

There is something to all this. U.S. alliances should exist not primarily as expressions of national altruism and largesse, but as ways of advancing America’s own interests. And alliances can indeed cease to make sense. Cold War alliances that did not have legs, like NATO’s stillborn cousins CENTO in the Middle East and SEATO in Southeast Asia, attest to this reality.

But the truth is that sustaining alliances in North America, Europe and maritime Asia does advance U.S. interests—even when looked at from a hard-nosed businessman’s point of view. The reality is that U.S. alliances have served and continue to serve as an enduring source of strategic advantage and leverage—and ultimately, added security—for America. Indeed, Washington’s network of pacts is the envy of America’s rivals. Its main strategic competitors would trade places with us because they recognize and value what many alliance naysayers increasingly discount: America’s web of foreign security relationships is a source of power and influence in the world. And in particular, America’s rivals understand that U.S. alliances have foreclosed their expansion or reassertion of spheres of influence through the use of military force.

In the longer term, prudently managed alliances can lead to fewer American lives lost and less money spent. But while U.S. alliances are indeed valuable, the skepticism of Trump, Obama and others should be taken as an important reminder that alliances require continuing scrutiny, revision and accommodation to realize their value and to appropriately correlate risks and costs to benefits. The United States urgently needs to update its thinking about alliances for a new era.

IN ESSENCE, America benefits from alliances because the world is a competitive place. The United States is stronger, more able to shape global affairs in important ways and ultimately safer when allied with like-minded countries in key regions than without them. Put simply, it is generally better to have powerful partners than not. It is a commonplace that a person backed by a network of like-minded associates is a more formidable character than one on his own. And it is certainly better not to have those states aligned with one’s rivals. Alliances allow the United States to agglomerate the power and wealth of affinitive states (or at least those sharing similar fears) for common, broadly liberal purposes, while locking out rivals which could otherwise leverage that same power and wealth, probably for illiberal ends. The West prevailed in the Cold War in large part because of the coherence and strength of its alliance in the face of the Soviet Union. George Shultz, remarking upon the central factor behind the end of the Cold War, attributed it to the Soviet leadership’s realization not only that the United States was resolved to continue and intensify the Cold War competition, but that its major allies in Europe and Japan were as well and that the USSR simply could no longer hope to match such a grouping in a sustained geostrategic competition.

No other like-minded country is strong enough to perform the United States’ leadership role in this alliance network. The United States is the only nation with the power, global reach, financial depth and standing to cohere and maintain such a diverse grouping for broadly liberal ends. Collective action is always difficult, but it is particularly challenging when dealing with states, and most so in the realm of security and defense. Indeed, the United States is the only country that can overmatch regional hegemonic aspirants like China and Russia. Without America’s involvement, the calculations of states under the shadow of Chinese and Russian power would be considerably different. With the United States, balancing against major regional states is a rational strategy; without it, bandwagoning and accommodation become considerably more compelling.

This is well and good, some might retort, but these alliances are more trouble than they are worth. The scope of threats and enemies an alliance network has to deal with is wider than if the United States cut itself free of its allies. A nation that spreads its security commitments too freely risks entrapment in wars that do not serve its national interests and liabilities that undermine the credibility of its commitments elsewhere, just as a business that takes on too many disparate subsidiaries risks losing focus on its core competency and, ultimately, its profitability. Thus it is not clear that the United States is, on balance, more secure by being in such a network. To these critics, the case for alliances is circular, since the United States simply ends up defending capable but threatened or conniving states that might otherwise fend for themselves from rivals with whom the United States might otherwise have cordial relations. Accordingly, they contend, the United States can withdraw from its alliance commitments and the world situation will not deteriorate in a way that matters enough to justify U.S. intervention; states will step up to take care of their own security. Moreover, even if the situation does deteriorate, the United States can always reintervene to redress the situation.

There is some potency to variants of this argument, but it is ultimately unpersuasive. It relies on assumptions that the United States has learned the hard way are imprudent to count upon. First, the world situation can indeed deteriorate when the United States pulls back, and can do so precipitously and unpredictably. Americans have run this experiment before—after World War I, when the United States withdrew from European affairs. Before 1914, Great Britain had, in its period of preeminence, played the role of the promoter and guarantor of broadly liberal interests. But, after the winnowing of the Great War and absent the unique power of the United States, like-minded countries like Britain and France were unable to deter or halt the rapacity of states like Germany and the Soviet Union during the interwar period.

Nor does one need to see a Hitler or Stalin around every geopolitical corner to fear that such deterioration might well happen again. Today’s Russia is clearly interested in reestablishing its suzerainty over its historical sphere of influence, and China increasingly seems keen to attain dominance in East and maritime Asia. Without the clear commitment of the world’s most powerful state to balancing and blocking these aspirations, it is only prudent to reckon that these states’ ambitions and assertiveness would grow, and that others would join them. It is worth remembering, after all, that Berlin and Moscow were not the only revisionist actors in the interwar period—there were also Tokyo, Rome and Budapest, to name just a few. Ambition and interest are largely elastic functions springing from perceptions of feasibility and affordability in geopolitics as in personal life. Better to meet—and, best, deter—threats when they are aborning and still more subject to counteraction and contraction rather than when they have had the chance to grow and metastasize. The logic is to shape and deter threats so that intrepid and enterprising states see that restraint is a wiser course than aggression.

Stability in the international system is the exception rather than the norm, particularly favorable peaceful stability characterized by respect for a rules-based liberal order. Balances do not mechanically self-generate. Without the involvement of the United States, it is not at all clear that European countries would band together to block Russian aggressiveness, or even that they would, over time and in increasingly dire economic and societal straits, avoid deepening tensions among themselves. Likewise, in Asia, it is by no means clear that regional states, awed by a massive China, would cohere to balance rather than bandwagon with it. Or that revanchist or aggressive nationalist impulses on the part of many states would not come to overtake more constructive foreign policies that favor the maintenance of a stable and attractive international security and economic order.

If such a deterioration were to happen, moreover, it would almost certainly implicate the United States, given its far-reaching interests, and likely drag Washington militarily back into these regions yet again. This is what happened after World War I, and again after World War II. After both conflicts, the United States demobilized its fighting forces and expected to return again to something approximating its traditional insular position, yet both times was drawn back into European and Asian affairs. Similarly, in any plausible future environment, if Europe were threatening to descend into acrimony or fall under Russian hegemony, or if Asia were looking likely to come under Beijing’s dominance, the United States would almost certainly want to prevent such outcomes from occurring. Washington would know that a nation or collection of nations that could agglomerate the power of the world’s most productive regions would also be one that could begin setting the terms of international order, including with respect to trade, the so-called “global commons,” international laws and norms, and values, as well as begin to project influence, power and military might out of these regions and into the Western Hemisphere.

Critics of America’s alliance posture—most notably, the “offshore balancing” school—might concede this, but they would argue that the United States could then intervene again in these regions to rectify the balance. The fundamental problem with this line of argument, as the Center for Strategic and Budgetary Assessment’s Evan Montgomery has shown, is that it underestimates the profound and potentially insuperable difficulties of regaining a military foothold in a region after having first withdrawn. In any circumstance, such an attempt would involve substantial collective-action problems stemming from skepticism about the reliability and sustainability of U.S. pledges—not unreasonable concerns since Washington had previously withdrawn—and due to the reality that such alliances would be far harder to reassemble than maintain.

These might all be manageable if the military challenges were not so severe. Even in situations in which the United States is the dominant military power, reentering a contested or defended region is generally far harder than maintaining one’s strong position next to capable allies within it. It was a lot harder for the United States to fight back into Fortress Europe, for instance, than it would have been to participate in a more serious defense of France in 1940, let alone 1936. This is particularly the case in today’s unfolding military-technological era, an age in which antiaccess/area denial (A2/AD) systems are giving an entrenched power new advantages against an opponent attempting to penetrate its defense umbrella.

Thus if China or Russia could establish broader military zones of influence in Asia or Europe, these spheres of dominance would be much costlier and harder to roll back than their creation would be to resist in the first place. From a strategic perspective, it makes more sense to maintain NATO and alliances with Asian maritime states, and prevent Moscow or Beijing from being able to establish dominance over their respective regions, than to withdraw and have to fight back into those theaters when these states have had the opportunity to establish fully mature no-entry zones.

The best way to achieve this deterrent effect is not only with paper alliances, but with deep, formalized and integrated allied military postures. Much of the reason for this is the important role of appropriately forward-deployed and, increasingly, forward-stationed forces for deterrence. As Jakub Grygiel and Wess Mitchell, of Johns Hopkins University and the Center for European Policy Analysis respectively, have demonstrated, forces on the vulnerable frontiers of Eurasia serve to preclude or foreclose an enterprising opponent’s opportunities for opportunistic expansion, perpetrated through fait accompli or coup de main strategies. In the absence of forward, combat-credible deterrence forces, such approaches could otherwise appear attractive if a potential aggressor reckons that he can bring a conflict to a close before his adversary—particularly the United States—can bring to bear the full weight of his military power. This is the logic, for instance, behind Russia’s so-called “escalate to deescalate” strategy, which is designed to bring a conflict to an end at a stage before the full preponderance of NATO’s expeditionary forces can be brought into the balance. Accordingly, forward basing is crucial to enabling effective and combat-credible military postures in key regions like Europe and East Asia. Without U.S. bases in Germany or Japan, for instance, U.S. military power in these two regions would be a shadow of what it is (and can, with reinforcements from the homeland, become).

Finally, some argue that American alliances are just too expensive to be borne. But expensive compared to what? As Washington Post columnist Robert Samuelson and others have argued, financial considerations should inform and shape but not override strategic calculations about U.S. alliances. For one thing, U.S. allies, while they could, certainly should and increasingly must contribute more to their defense, do defray the costs of U.S. forces through a variety of mechanisms such as basing and host-nation support. More fundamentally, the costs of alliances and the military and other requirements they generate are certainly substantial, but within America’s resource capacity to pay. Indeed, defense and related costs represent a much lower fraction of national expenditure than they have in the past. Defense spending consumed on the order of one-sixth of GDP in the early 1950s; today it is more like one twenty-fifth.

Moreover, even under the rosiest scenarios, curtailing America’s alliance military commitments would save something in the vicinity of 1 percent of GDP, yet the savings might well be offset by higher overall U.S. military spending to prepare forces to fight their way back into overseas theaters where it would continue to have vital interests. As some proponents of offshore balancing recognize, a military that can penetrate back into key regions once rivals like China or Russia have established dominance over them would be a more demanding standard for defense requirements than today’s, likely driving up costs even without a war breaking out.

The costs of such a policy failing would be far higher than any savings gained. It was certainly more expensive to build up the U.S. military of World War II than it would have been had Washington sustained a post–World War I armed force capable of deterring or at least confining the attacks of Germany and Japan. Paradoxically, shedding alliance commitments could result in the United States having to pay higher military “insurance premiums” as the price of living in what would likely be a far more unstable and unpredictable global security environment. The logic of retrenchment, as some proponents such as Hugh White readily concede, actually would likely necessitate a higher level of military spending for countries that must now go it alone, with all the costs that unilateral military postures entail.

Fundamentally, then, the financial expense of America’s strategic architecture of alliances should only be viewed against its more unilateral alternatives, including their “life cycle” costs. Thus, genuine strategic need should drive posture; considerations of economy should inform, shape and constrain it, rather than the other way around. As Adam Smith put it, defense is more important than opulence. America does not need to sacrifice its prosperity for an effective alliance posture, but Washington should not seek to wring every penny out of it either.

AMERICA HAS developed and sustained an extraordinary network of allies whose collective strength and will pose an enduring deterrent to any state or states contemplating aggression or coercion. Certainly U.S. involvement in and leadership of this set of alliances pose risks and generate costs, but so too would abandonment of them—and these latter risks are likely higher, and considerably so, than the ones assumed by sticking with the present course. And if the ultimate recourse offered by critics of U.S. alliances to the failure of their policy of retrenchment is to fight back into these regions and redevelop these relationships—in other words, to end up at square one, but bloodied and with hard-earned credibility diminished—why, then, should the United States abandon its alliances in the first place? Rather than backing out, is it not better to tend to and improve them while making them more equitable rather than go through all the transaction costs, broken trust and pain of severing or weakening them?

But the status quo is not sustainable either. Things will have to change to remain the same. Here, both Trump and Obama have touched on real problems that need to be addressed: allies’ free riding in an era of austerity, in which standards of living have been stagnant for too many Americans; security risks that exceed in some cases their costs; and allies that appear increasingly hesitant or unwilling to fight for their own sovereignty and freedom. Dumping allies wholesale is not the answer, but neither is stasis. The solution is to redefine America’s security relationships and transform its moribund protectorate relationships into true security partnerships. This demanding task, which awaits the next president, must take place in an era of renewed competition when it comes to global security cooperation, in which current and potential U.S. allies have their own options and will pursue their own interests, and countries like China and Russia are actively seeking openings to establish their own overseas security relationships.

How, then, might America extend its alliance advantage and put it on a more equitable and sustainable footing? First, Washington needs to remind its allies, and itself, that alliances are two-way commitments, which by their nature demand quid pro quos. They will only last as long as voters in democracies like the United States and in its allied countries continue to believe in their “value proposition.” Allies doing more for themselves is not only practically useful, but also serves as a signal of their own commitment to mutual security goals, which in turn increases the value Americans see in an alliance, especially in an environment in which Americans are again being asked to assume greater risks in light of a resurgent Russia and rising China. This requires allies to raise their defense spending and more equitably share in the risks and responsibilities of the pact. NATO countries as well as Asian allies must spend more, and spend it on genuine combat-credible military forces, intelligence and internal security capabilities to address unconventional, conventional, cyber and WMD threats. The days of smaller allies spending precious resources on outsized prestige capabilities like high-end fighter aircraft and frigates that do not actually contribute to the local-security bottom line, or on token “out of area” expeditionary forces in an attempt to curry favor with the United States, are long over. Allies must adopt a back-to-basics approach that places priority, first and foremost, on shoring up their internal and territorial security, including territorial waters, airspace and communications networks. At the same time, Washington must be more disciplined in pressing allies to focus their investments on these efforts rather than pressing them to buy American systems of questionable utility.

Furthermore, reciprocity matters. No longer is Washington dealing with a supine postwar Europe and Asia but rather an EU that has a larger economy than the United States and a Japan that boasts the world’s third-largest economy. Thus, if Americans must be prepared to come to the aid of allies, should not allies be prepared to come to the assistance of the United States if its people or forces are attacked? Absolutely. And that is why Washington should support Prime Minister Shinzo Abe of Japan, who has pushed through historic legislation in recent years to allow Japan to come to the aid of U.S. forces even where Japan itself has not been attacked.

Washington also needs to get the theory of the case right when it comes to the basic division of labor between the United States and its frontline allies. In light of the growing military challenge posed by potential opponents like Russia and China, armed as they increasingly are with formidable A2/AD architectures and rapidly deployable maneuver forces, the United States needs to encourage frontline allies in Europe and Asia to take a page from Moscow and Beijing’s playbooks. U.S. allies must develop their own A2/AD complexes in order to block or complicate easy seizures and to be more capable by themselves as first responders, especially in responding to “gray zone” situations. In particular, these states must do more to guard against unconventional and paramilitary threats, which are important components of the strategies of revisionist powers like Russia and China. This approach will necessitate allies focusing on the development of improved internal security, law enforcement, border police and coast-guard capabilities that stretch beyond the purely military domain. And it will require Washington prioritizing American unconventional-warfare capabilities, resident in the Army’s Special Forces, to advise and assist frontline states in dealing with ambiguous threats that fall short of clear military action. Frontline states must also do more to shore up their ability to provide areas relatively secure from missile or air attacks in which crucial U.S. forces flowing in can disembark and quickly maneuver. Fortunately, in encouraging these efforts the United States will, in many cases, be pushing on an open door, as the Baltic states, Poland, Japan and the Philippines are already taking initial steps in this direction.

As America’s allies become more capable of defending themselves by adopting modern technologies that deny the use of key warfighting domains—land, air, sea, space and cyberspace—to potential aggressors, the United States can better focus on two overarching military missions. First, the United States is the only country for the foreseeable future that can guard the so-called global commons—those vital arteries running across the oceans, through the air, undersea in the form of cables and gas pipelines, and through space that allow goods, services, information and people to flow safely. Those commons will be increasingly under threat from terrorists and revisionist powers alike, and their security cannot be taken for granted. Because U.S. allies have as much, if not more, of a stake in maintaining the freedom of the commons, they see tremendous value in the United States maintaining military forces to police them.

Second, the United States plays an indispensable role as a global swing force across the regions of the world. Wars can break out in any theater—or across multiple theaters at once. Yet the United States is the only country that possesses a full suite of global surveillance and strike forces in the form of stealthy, penetrating, long-range surveillance and strike aircraft, submarines and unmanned underwater vehicles, special-operations forces, cyber and electronic attack capabilities, as well as precision missiles and other munitions. These forces can deliver conventional, nuclear or nonkinetic strikes anywhere on the planet, and are a vital component of deterrence for the United States and its allies in the event of serious conflict with a highly capable opponent like Russia or China. The problem is that, while the United States is unique in its ability to provide global surveillance and strike forces, the proliferation of A2/AD capabilities necessitates new investments, including both land- and sea-based options, to ensure that the U.S. military will have qualitatively superior capabilities in sufficient numbers to make good on its global deterrence commitments in the years ahead. A new division of labor between allies and the United States should serve to free up resources for the United States to focus on maintaining its upper hand in this vital realm of global surveillance and strike capability.

Lastly, the United States must reaffirm the importance of extended nuclear deterrence and ensure its continued credibility. In particular, it must ensure that it has viable limitable and discriminate nuclear options to deter an adversary’s limited use of nuclear weapons so that the United States is never forced into a “suicide or surrender” situation over a distant ally. Washington should want to foreclose opportunities for hostile powers to ever see an opening where their limited use of nuclear weapons could reasonably be seen to yield advantages.

As part of this effort to maintain the credibility of its extended nuclear deterrent, the United States should also be willing to explore new methods of involving allies in its nuclear posture. This is already well established in NATO, where many of the allies participate in the nuclear mission by basing U.S. nuclear weapons, preparing for their delivery in wartime or committing to nonnuclear military operations to enable effective nuclear delivery. Such “nuclear-sharing” arrangements demonstrate that allies are willing to share the risks, costs and sometimes the opprobrium of shouldering the collective allied nuclear deterrent.

Taken together, the measures proposed here could help to revitalize existing alliances and put them on a firmer and more equitable footing. The era of complacency—both conceptual and financial—is over. Both the United States and its allies will have to do more to extract value from their common alliances and to redress the concerns raised by alliance skeptics lest these lead to strategic decoupling—and the advent of a far less stable world and a more menacing security environment.

THE UNITED STATES has assembled and maintained the most impressive alliance system the world has ever seen, a system that has been crucial in building and protecting a world order conducive to its security, friendly to its interests and congenial to its values. Constructing and maintaining this system has often involved sacrifices and not a few mistakes, and even compromise of interests Washington might otherwise have pressed. But it has served larger and longer-term interests. It has been an exercise in, to use Adam Smith’s old phrase, enlightened self-interest—a focus on the likely cumulative results of policies, rather than on their immediate debits and credits. For a uniquely powerful and great nation, this remains the best lens through which to evaluate America’s international policies, especially on issues where the penalties for error are so grim.

Lord Salisbury pointed out that the most common mistake in politics is sticking to the carcass of dead policies. It is certainly prudent to revisit long-standing ones. Inertia and sentimentality are no justifications for policies that risk American lives and wealth. But U.S. alliances do meet the searching scrutiny that should be applied to them. They surely involve costs, risks and inequities, but they also yield great benefits, and their realistic alternatives entail even greater hazards and uncertainties. Better to cultivate and adapt them than to cavalierly toss them away.

Elbridge Colby is the Robert M. Gates Senior Fellow at the Center for a New American Security. Jim Thomas is a principal with the Telemus Group and former deputy assistant secretary of defense for resources and plans.

Image: Polish army military police​ soldiers during exercise Steadfast Jazz 2013. Flickr/U.S. Army Europe