Since the dawn of the nuclear age, the United States has extended its “nuclear umbrella” over its closest allies. This nuclear umbrella, also referred to as an “extended deterrent,” means that the U.S. guarantees the security of a close ally—including through the use of nuclear weapons. Put simply, extended deterrence means that if an adversary carries out a strategic attack on an American ally or otherwise threatens to topple said ally through conventional means, the United States reserves the right to defend that ally with all the forces at its disposal, to include its nuclear arsenal. Generally speaking, the states that are under the American nuclear umbrella are U.S. allies in NATO, Australia, Japan, and South Korea.REF

Today, the fear of a withdrawal of America’s extended-deterrent guarantee to its closest allies is triggering actors from Poland to Korea to France to consider building their own, independent nuclear arsenals to guarantee their own security or to extend their own sovereign strategic capabilities over other allies as a means of establishing their own nuclear umbrella.REF It might seem odd that the United States extends its nuclear umbrella over other nations—seemingly, this puts the U.S. at greater risk of a nuclear attack as it defends a foreign power—with little-to-no overt benefit for the United States. But the reason for extending America’s nuclear umbrella over its closest allies is not altruism, but because doing so squarely serves U.S. national interests and makes war—including nuclear war—less likely for the U.S.

Indeed, extending the nuclear umbrella provides a variety of benefits to the United States, to include giving America greater influence over the actions of its foreign allies; reducing the incentive for other states to pursue nuclear weapons (and therefore reducing the chance that the United States will become involved in a nuclear war); and incentivizing direct foreign investment into the U.S. economy and U.S. markets. Most importantly, though, America’s nuclear umbrella is a deeply stabilizing force on global security and enables Americans to enjoy family, faith, and prosperity in peace.

Extended Deterrence Gives the U.S. More Influence

One of the most obvious benefits of America’s nuclear umbrella is that it gives the United States significant leverage over those states that are underneath said umbrella. Foreign capitals, seeking to maintain their place under the American nuclear umbrella, often acquiesce to Washington’s policy preferences, be they in security issues, trade policies, or diplomacy. This soft power is shown at various international fora, where allies often side with the United States on a host of issues and co-sponsor resolutions that serve American interests.REF

Further, extended deterrence is in many ways a two-way street. Allies, in exchange for the extended-deterrent umbrella, augment American military power. As an example, South Korea, which has been under the American extended deterrent umbrella since the 1950s, has not only fought with the United States in every war since the Korean War but also has one of the strongest defense industrial bases in the free world, possesses a very large and credible army, and gives the U.S. important basing access from which it can generate combat power.REF Taken together, the alliance with South Korea gives the United States a veritable Gibraltar on the Asian mainland.

Similarly, America’s alliance with Japan—to include the nuclear component—provides the United States with an ally that has the second-largest navy in the Western Pacific and a highly competent air force that is capable of conducting strikes across the Western Pacific and East Asia, along with the military bases needed for any long-haul flights from the continental United States.

Europe, with all its problems—and they are many—similarly gives the United States important access from which the U.S. military can conduct a variety of operations that directly benefit U.S. interests. These include the forward stationing of missile defense batteries that can destroy Iranian missile threats, forward deployment of air assets that are critical to targeting and destroying terror threats, maritime bases that allow the U.S. Navy unfettered access to the Mediterranean and Red Seas, and nuclear weapons bases that allow the United States to deter strategic attack by America’s enemies.

Further, European militaries, particularly those in Poland and the Baltic and Nordic nations, are rearming.REF Even Germany has begun a significant rearmament program, long overdue though it is.REF Indeed, one of the reasons that Europe is taking security issues seriously and rearming is out of a fear of the United States withdrawing its nuclear umbrella from its NATO allies if Europe does not contribute more to the NATO alliance in the form of credible combat power.REF

While there may be some benefits to U.S. allies having an independent nuclear arsenal, the downsides of a more proliferated world probably outweigh the upsides. Indeed, the United States may already be seeing the rumblings of states who are less willing to acquiesce or accommodate American security preferences as they seek their own independent (or at least non-American) nuclear umbrellas.REF This loss of influence would track with the historical record, when Washington lost significant amounts of influence over decision-making in Paris, following France’s joining of the nuclear club in the early 1960s.REF

The Nuclear Umbrella Attracts Foreign Investment

Perhaps unsurprisingly, the more secure a state feels, the more prosperous it becomes. The more prosperous it becomes, the more willing it is to invest. This lesson from throughout history continues today.

The top five direct investors in the United States are all close treaty allies currently underneath the American nuclear umbrella.REF It should not be forgotten that extended deterrence often takes the treaty form of a “mutual security” pact, as is the case with the United States and Korea, the United States and Japan, and the broad array of networks within NATO. As demonstrated, a mutual defense treaty is not just a one-sided “the United States gives and others take” agreement. It is a pledge to come to each other’s aid.

Think of the neighborhood bully, China, shaking down other countries and threatening them. The United States teaming up with Japan and South Korea for security means that China is less likely to hurt U.S. neighbors, thereby allowing the United States to increase trade with those neighbors to everyone’s direct and mutual economic benefit. Indeed, in the late 1950s, South Korea and sub-Saharan Africa had the same per capita gross domestic product.REF

Today, South Korea is the 14th-largest economy in the worldREF and one of the most digitally integrated societies on the planetREF—in no small part because of America’s security guarantee and the extended deterrent commitment. This has not only benefited South Korea’s economy—but also the American economy, both due to trade that is mutually beneficial and because of Korea’s direct foreign investment in the U.S. economy. Similar stories unfold with most allies who enjoy America’s extended-deterrent guarantee.

In the final analysis, more security means more investment and prosperity for all, because businesses and investors like stability and certainty. Other countries feel safe investing in the United States because America is strong and its political system is stable. And Americans feel safe investing abroad (and making a tidy profit in the process) knowing that their allies are safe and their investments will be secure in the long term.

Extended Deterrence Reduces Nuclear War

If the United States withdrew its extended-deterrent guarantee from its allies in NATO and East Asia—or, if those states no longer believed in the efficacy of those guarantees—then it should be expected that some, perhaps many, of those states would acquire indigenous nuclear weapons capabilities. Indeed, Germany, Japan, Poland, South Korea, and others may well have sought or desired indigenous nuclear weapons programs but have deferred such plans over the past half century in large part because of the U.S. nuclear umbrella.

If those countries had nuclear arms, the United States would likely see some additional deterrence benefit. Adversaries may be better deterred by the prospects of additional nuclear powers. But there are two very significant downsides to such a world. The first is that selective nuclear proliferation would almost certainly not be limited to U.S. allies. Other powers would likely respond and seek their own nuclear arsenals in response to these new nuclear powers. For each nuclear-armed Germany, Japan, Poland, or South Korea, the world could see a nuclear-armed Burma, Saudi Arabia, Venezuela, or Vietnam. And there is no reason why such a proliferation cascade would stop at only a handful of countries.

The second downside is that in a world that no longer had fewer than 10 nuclear weapons states, as is the case today, but one with two or three times as many nuclear powers, the prospect for a state-on-state conflict escalating to the nuclear threshold would likely increase.REF Nuclear-armed states that had the option of escalating might be deterred from using nuclear weapons—but would all of those states make that decision? Or might a subset of them feel compelled to employ nuclear weapons in a conflict in order to achieve operational advantage or merely to stave off conventional defeat?

In such a nuclear proliferated world, the likelihood of nuclear war would increase, which could have adverse consequences for the United States—not least of which is that the United States could become embroiled in such a war. This could occur by being pulled into the conflict (either before or after first nuclear employment), or the conflict could expand to other, seemingly uninvolved powers with great rapidity and for little apparent reason. Who can forget that World War I began because a Serbian terrorist assassinated an Austrian Archduke—and dragged the British Empire, France, Imperial Germany, Italy, Czarist Russia, the Turkish Empire, the United States, and many others into the war—resulting in the collapse of four empires and upwards of 14 million dead.REF Now imagine such a war, but with half the participants having nuclear weapons as part of their arsenals.

It is tempting to say that even if medium-sized nuclear-armed powers in Asia, Europe, or the Middle East got into a conflict, the United States could remain aloof and uninvolved: That may be true for some conflicts. But it is difficult to forecast with any degree of accuracy how a nuclear war between two or even multiple nuclear-armed adversaries—some subset of which are not in the American orbit or under the U.S. nuclear umbrella—would end. The United States may get dragged into such a war, even if the United States did not want to get involved (as was the case in World War I and World War II). Indeed, history is replete with nations getting dragged into wars that they otherwise would like to ignore.

Even if the United States was able to maintain its neutrality, the consequence of a multi-sided nuclear war could well be a radical change in the world’s security environment—to include potentially a security order that is far, far less friendly than the one the United States enjoys today. Indeed, additional nuclear wars among non-U.S. partners could well have long-term consequences for the United States that one cannot yet determine—but are unlikely to be to the benefit of the American people and could well imperil that very peace that they so desperately seek and deserve.

Conclusion

In the end, extended deterrence is a stabilizing force that allows Americans to focus on things that matter directly to them: security, peace, prosperity, family, and faith. It does this by increasing the freedom of action of the United States and increasing foreign direct investment into the American economy, but most importantly, it makes war (particularly, nuclear war) less likely by deterring aggression.

A world without the American nuclear umbrella is a world with more nuclear powers and more nuclear wars—one with unforeseen downsides for the United States and the American people. It is for that reason that since 1947 the United States, across Republican and Democrat administrations, has extended its nuclear umbrella over its closest allies.

Robert Peters is a Senior Research Fellow for Strategic Deterrence for Douglas and Sarah Allison Center for National Security at The Heritage Foundation.