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.