Editor’s Note: Please take a look at Elbridge Colby’s recent debate with T. X. Hammes: AirSea Battle vs. Offshore Control.

In a thoughtful and provocative January essay, David Santoro argues that America’s East Asian allies are likely to face increasing incentives to throw off their nonproliferation straitjacket and seek to obtain nuclear weapons if North Korean belligerence worsens and China’s ambitious assertiveness waxes. Santoro contends that, if Tokyo or Seoul elect to pursue nuclear weapons of their own, Washington will be faced with a stark choice. On the one hand, the United States could swallow the bitter pill of indigenous allied nuclear weapons capabilities, the development of which Washington has opposed, for the sake of what he terms “geopolitical” considerations. Or, on the other hand, Washington could hold true to the nonproliferation gospel that any further proliferation is too perilous to regional stability and menacing to the nonproliferation order, and so take the road of “terminating its alliances.” Santoro admirably doesn’t beat around the bush and forthrightly argues that, in the event U.S. allies like Japan or South Korea make for a nuclear weapons capability, Washington should “cut them adrift” and end its alliances with them. In his words, nonproliferation should trump geopolitics.

Santoro is to be commended for making his case clearly and for highlighting the increasingly pressing question of how to address U.S. allies’ disquiet about the reliability and credibility of our extended deterrent. But he is wrong to argue that we should, in all or even most of the variants of the scenario he posits, terminate our alliances with Japan or South Korea if they pursue nuclear weapons.

More broadly, he is wrong to contend that nonproliferation should trump geopolitics. Santoro is wrong because there are numerous plausible scenarios in which it would be ill-advised and perhaps even foolhardy for the United States to abandon its long-established and valuable alliances with two of the world’s largest powers for the sake of a principle that, while certainly valid and thus worth pursuing, should not be held as the highest good of U.S. foreign policy. In other words, geopolitics should trump nonproliferation.

Why? Because the specific characteristics of American foreign policy, including its alliance relationships and its nonproliferation policies, should not be fixed but, like Aristotelian morality, should be determined by reference to a more fundamental focus—in the case of U.S. foreign policy, on the broad-minded defense of Americans’ lives, liberties and prosperity, and on the enlightened advancement of their interests in the international arena. And, because the world is ever-changing—with new powers rising and old powers falling, new threats emerging and old ones falling away, and new opportunities opening and old ones closing—the specific characteristics of the fulfillment of this broad mandate are inherently subject to change. Thus American foreign policy should be—or, more accurately, must be—guided by elastic political judgment rather than marble dictates, steered by continual recalculation of how to pursue these core national aims in light of a changing international landscape the dimensions of which impose the necessity of choices among goods.

This is of direct relevance in the scenario Santoro paints. Nonproliferation is unquestionably a great good. Contra Kenneth Waltz, the world is almost certainly better off with fewer rather than more nuclear-weapons states for all the reasons that Presidents George W. Bush and Barack Obama, analysts like Scott Sagan, and many others have amply elucidated. Moreover, it is of particular value for the United States, as nonproliferation helps Washington maintain the leverage it enjoys as one of the only nuclear powers, and one of only two nuclear superpowers.

But while nonproliferation is certainly a (quite substantial) good, it is not the good; it is not the summum bonum of American foreign policy. Rather, the summum bonum of American foreign policy is security in liberty and prosperity. Nonproliferation is a means to that end, not its fulfillment, and is only one of many such means. Alliances, for instance with Japan and South Korea, are also goods designed to serve that broad purpose of American foreign policy, and are goods that may in certain circumstances be more important to the service of that higher aim than unyielding adherence to nonproliferation goals. And so the reality is that unswerving fidelity to the principle of nonproliferation may not always be advisable in light of broader American foreign policy considerations—and indeed might actually detract from them. In simpler terms, it may make sense in certain circumstances for the United States to accept proliferation rather than to oppose it unconditionally.

The crucial premise for this proposition is that proliferation can be tolerable, in the sense of something that one might not like but can be endured. If proliferation inexorably led to disaster, then Santoro would be right. But it need not. Rather, it can, at least in certain circumstances, be managed. How do we know this? At the level of common sense and of theory, we know that nations are usually self-interested and survivalist, and usually seek to obtain nuclear weapons either for security and deterrence or for prestige (or for some combination thereof). The United States can reckon with states that act like this, especially if they are friendly to us, even if that reckoning is harder or less in our favor once they have nuclear arsenals of their own.

Experience supports this assessment. Past is not always prologue, but proliferation has happened before, particularly among U.S. allies, without devastating or even significantly undermining U.S. security interests. Great Britain and France both acquired nuclear weapons during the Cold War, surely complicating U.S. strategy but demonstrably not negating it—after all, the Soviet Union didn’t attack, nuclear war didn’t start, and follow-on proliferation didn’t occur in Europe (although admittedly the last did not come to pass due in large part to active U.S. efforts to stem it, particularly in the case of Germany). Indeed, if we are to believe NATO’s official documents, such proliferation actually “contributed” to the Alliance’s security. In the Middle East, meanwhile, declassified documents indicate that President Nixon—and, by extension, his successors—have believed that they “could live” with Israel’s alleged nuclear-weapons program. This seems to have been a reasonable proposition, as Israel has never flaunted any such capabilities but the widespread belief that they exist has likely contributed to Israel’s deterrent and to its neighbors’ conviction that it needed to be accepted as a permanent feature of the region. Even proliferation to our enemies—such as the USSR and Mao’s China—has been, while clearly a grave blow to our security and our strategic position, nonetheless tolerable. Despite Moscow and Beijing gaining nuclear weapons—indubitably major setbacks to U.S. security—deterrence nevertheless held. So history indicates that proliferation can be managed.

Why should we think the future will be different? Certainly we should expect proliferation to be, at the very least, a serious challenge to the international order and, when to our enemies, a dangerous and possibly very grave development. But why shouldn’t we expect it to be, at least in some circumstances, nonetheless manageable, something to be traded against other important interests? Needless to say, proliferation to a madman or a grotesquely irresponsible regime could well be catastrophic, but why should we expect it to be so if to states with established, responsible governments—states like Japan and South Korea? In light of this, it seems reasonable to judge that, in the future as in the past, proliferation may be, while distasteful or even seriously harmful, nonetheless sometimes tolerable. And the reality that proliferation may be tolerable simply means that nonproliferation is, while justifiably a high priority, nonetheless a tradable, instrumental good.

If this is so, then determining when to prioritize nonproliferation requires that we weigh its benefits and costs in specific cases—in other words, that we make political judgments about how avidly to pursue it. And the reality is that, in some and perhaps many cases, pursuing nonproliferation to the hilt may not be worth the attendant costs and risks. This could hold true not only because the costs could be high—for instance, an ally might react negatively by cutting an alliance tie, pursuing an autonomous foreign policy, or bandwagoning with an adversary—but also because the benefits could be low, not only because the gains could themselves be modest but also because U.S. opposition might be ineffectual or even feckless, simply poisoning a relationship without succeeding in its purpose.

Pursuit of a nuclear weapons capability by Japan or South Korea could well present just such a case. Let us take Santoro’s scenario, in which a Japan or a South Korea of more or less their current political complexion decides to set out to build a nuclear weapon due to growing concerns about its security in light of threats from North Korea and/or China and because of rising skepticism about the reliability and efficacy of U.S. extended-deterrent guarantees. How would the United States calculate the costs and benefits of unyielding opposition to such a decision?

The first thing to observe is that Washington’s response would not need to be so binary as Santoro’s article suggests. After all, policy almost always takes place in the spectrum between extremes, avoiding, when and where possible, final decisions, and seeking to achieve goals with means short of the drastic. And termination of an alliance is one of the more drastic steps a state could take. Thus, the United States could and, in most plausible cases, quite reasonably would oppose independent Japanese or South Korean arsenals—but without taking that opposition to the point of terminating the alliance absent a broader divergence of interests. And that opposition might still reasonably be quite strenuous—Washington might well think it worthwhile to bend its alliances with Tokyo and Seoul quite far to see if it could achieve its nonproliferation goals, even if it ultimately decided not to break them. And the United States would have inducements at its disposal as well punishments. For instance, Washington might in the future consider extending new “nuclear sharing” arrangements to seek to deepen Japan or South Korea’s investment in U.S. nuclear deterrence as an alternative to autonomous weapons program. Nor should we expect such a course of action to be a recipe for failure. U.S. allies like Germany and, in point of fact, Japan have responded to such strong but limited suasion in the past and shelved plans to pursue independent nuclear forces. At the very least, such an approach could serve as a way of raising the bar to test whether Tokyo or Seoul was truly in earnest, and could weed out less serious and firmly-rooted pushes for an independent nuclear arsenal.

But what if Tokyo or Seoul were in fact in earnest, and ready to go the final mile to obtain its own arsenal, even at the cost of breaking the alliance with Washington? Would the benefits of pursuing Santoro’s recommended course of action outweigh the costs?

On the cost side, we can assume that wholly opposing either ally’s resolute decision to pursue nuclear weapons would put substantial pressure on our bilateral relations. It might well undermine them entirely if Tokyo or Seoul were truly determined to obtain its own nuclear arsenal, a prospect Santoro is ready to embrace in the event the choice needed to be made. But we must bear in mind the costs of such a course of action, which would likely have enormous strategic implications for the United States. Though U.S. policymakers and experts often like to state that U.S. alliances restrain proliferation among our allies, these alliances are not primarily nonproliferation instruments. Rather, they are geopolitical instruments designed to strengthen America’s position in the world and thus increase American security. Nonproliferation objectives are a part of that broader purpose, but only a part—and should be subordinated to and serve that broader goal.

And, in point of fact, U.S. alliances with Tokyo and Seoul do have far larger and, indeed, more important goals than simply restraining Japan and the ROK’s nuclear ambitions. Rather, U.S. alliances with Japan and South Korea are cornerstones of the whole U.S. position in Asia. The two countries host the bulk of U.S. bases in the region and their defense forces are major multipliers and legitimizers for Washington. Diplomatically, the alliances help anchor the U.S. presence in Asia. Now, if there were no serious challenges to U.S. interests in the Asia-Pacific, abandoning such equities might make sense, since there would be no need for them in such a benignly pacific region. But that is not the case. The United States faces in Asia not only an aggressive, nuclear-armed North Korea but, far more importantly, the rise of a mighty China which Washington will need to balance for the foreseeable future. In order to meet these challenges successfully, the United States will need allies like Japan and South Korea (just as they will need the United States). Terminating our alliances with Tokyo or Seoul would dramatically undermine these broader strategic objectives. Indeed, we could well expect the costs of cutting our alliances in such circumstances to be particularly high since it would likely be precisely intensified North Korean belligerence and/or growing Chinese assertiveness—and the calculation that the U.S. extended deterrent was insufficient to check them—that would impel Tokyo or Seoul’s decision to pursue a nuclear weapons program. Abandoning our alliance just as our ally was demonstrating its increasing skepticism about the sufficiency of our guarantees would likely exacerbate rather than alleviate the very tensions and instability we would be seeking to control.

Thus the costs of unyieldingly opposing such proliferation might be very high. But at the same time the benefits of such an approach might well be relatively low. The primary reason might simply be that U.S. opposition might not translate into much real influence over either Tokyo or Seoul should they elect to “go nuclear.” When the United States squeezed the ROK to halt its autonomous nuclear weapons program in the 1970s, Washington enjoyed overwhelming strategic, military, and economic leverage over Seoul. In the future that will no longer be the case, as South Korea is now one of the globe’s largest and most advanced economies, dwarfing its atavistic northern twin. Washington enjoys probably even less direct leverage over Tokyo, which, despite the Fukushima disaster, boasts one of the world’s largest and most sophisticated nuclear energy infrastructures, a top-notch space launch program, and presides over the globe’s third-largest economy. If Tokyo or Seoul were truly resolved to develop a nuclear weapons capability, especially in the face of threats that drew a decent degree of sympathy or at least quiet understanding in the international arena, it is questionable whether Washington could stop such an effort. Indeed, given that Washington agrees with Seoul and Tokyo about the nature and gravity of the threats most likely to push either one to pursue nuclear weapons of its own, how persuasive would Washington’s opposition be in such circumstances—especially given that the near-tautological premise of such a decision would be that the U.S. extended deterrent was not proving sufficiently credible or effective? The answer is that Washington’s degree of influence might be limited, and perhaps quite limited. Thus, in such instances, even if Washington did not like an autonomous nuclear capability in the hands of Tokyo or Seoul, it might be better off by making a virtue of necessity and ultimately accept it.

Of course we must recall there would be benefits to opposing even resolute pursuit of nuclear weapons by Japan or South Korea and serious costs in not doing so. Washington would indubitably find itself under intense pressure to hold the line against Japanese or South Korean proliferation in order to protect the Nuclear Nonproliferation Treaty-grounded nonproliferation order, which has managed (mostly) to stem proliferation in the decades since its creation. By opposing Japanese or South Korean pursuit of a weapons capability, the United States would demonstrate its commitment to the NPT and to nonproliferation in general, a stance that would undoubtedly resonate beneficially throughout Asia, the Middle East, and elsewhere. But even these real advantages might well not outweigh the costs of an unyielding opposition to Tokyo or Seoul’s pursuit of an autonomous nuclear arsenal.

Needless to say, these are only a few of the most salient factors Washington would need to consider in determining how strenuously to push its nonproliferation policies in the event of a Japanese or South Korean weapons program. Washington would also have to take into account the economic realm, for example. The essential point, however, is simply that Washington’s cost-benefit calculus might well, in certain circumstances, tell in favor of relenting to Tokyo or Seoul obtaining an independent nuclear weapons arsenal.

This is emphatically not to say that the United States should always or presumptively support a Japanese or South Korean nuclear weapons program. To the contrary: in many eventualities, an attempt by either nation to pursue nuclear weapons would be decidedly against U.S. interests and thus should result in intense U.S. opposition. This would clearly be the case if Japan or South Korea fell under an aggressive and hostile government and even in less dramatic cases, such as if the security threat from North Korea and China receded. In such cases pursuit of nuclear arms by Tokyo or Seoul would justifiably provoke Washington to prompt a serious showdown in alliance relations—and might well be grounds for termination of the alliance if Tokyo or Seoul refused to cooperate. And in almost all cases it would be proper and sensible for Washington to oppose autonomous Japanese or South Korean programs, even if not to the hilt. At the very least, allies like Japan and South Korea should—and certainly do—understand that pursuit of independent nuclear weapons capabilities stand a very good chance of jeopardizing their ties with Washington. This doubt should—and does—act as a brake on any such ambitions.

But the fact remains that there are instances, including quite cognizable instances, in which it would make sense for Washington ultimately to accede to an autonomous Japanese or South Korean nuclear arsenal. This is simply another way of saying that, in determining how to respond to a Japanese or South Korean nuclear weapons program, Washington would need to weigh costs and benefits, examining why Tokyo or Seoul was pursuing such a capability, the broader strategic context the United States faced, how much Washington needed from Japan or the ROK in the unfolding strategic landscape, the likely response of Tokyo or Seoul as well as others actors in Asia and beyond, the degree of U.S. leverage, and so forth. In briefer terms, it is to say that Washington would need to make a geopolitical decision about how to respond.

Of course a geopolitical calculus might well lead Washington to prioritize nonproliferation. But the point of this article is that it might not. David Santoro has commendably made the case for the nonproliferation uber alles point of view. And he has taken that viewpoint to its logical conclusion, which is that nonproliferation virtue should trump geopolitical camaraderie even when strategic logic would guide us to subordinate the former to the latter. Santoro is not wrong that nonproliferation is a great good, much to be guarded and advanced. But, as Raymond Aron put it, the most difficult questions of statecraft are not between “the good and the evil, but between the preferable and the detestable.” Clearly, further proliferation—even to our allies—would represent a blow to our interests. But to determine whether it would be detestable or only lamentable, we would need to examine the totality of the situation, weigh the benefits, costs, opportunities, and risks, and then decide whether prioritizing nonproliferation above the continuation of our alliances made sense.

In the case of Japan or South Korea arming against a more ferocious North Korea or a more aggressive China, it seems clear that there are scenarios in which we would reasonably determine that tolerance of the ills of further proliferation would be justified by the greater good of maintaining our alliances. Santoro’s prescription that we jettison our alliances for the sake of nonproliferation probity is like the Kantian’s who argues that you must not lie even to save your country. But those who are vested with the responsibility of leading our country in an enduringly uncertain and dangerous world cannot be guided by such counsels of perfection. Rather, they should adhere to the old axiom: to hold fast to the central purpose of American statecraft—that of protecting Americans’ security, liberty, and prosperity through moral means—and, in pursuit of that noble aim, to allow every other good to fall where it may.

Elbridge Colby is a Fellow at the Center for a New American Security. Follow him on Twitter: @ElbridgeColby.