Trusting Security Assurances

Nuclear weapons can offer considerable security to countries that possess them; attacking a country that has nuclear weapons bears a far greater risk than attacking a country that lacks them. Yet most countries agree that more nuclear weapons in the world means a higher likelihood that one will eventually be used, with catastrophic consequences. Given this risk, governments worldwide have worked to limit the proliferation of nuclear weapons. Diplomatic efforts, such as the Nuclear Nonproliferation Treaty (NPT), have secured agreements from member countries that possess nuclear weapons to reduce their stockpiles. The NPT also ensures that non-nuclearized states do not develop weapons capabilities in the first place. 

The NPT has strengthened global norms against developing nuclear weapons. Yet the agreement is voluntary. Countries that fear for their security or wish to exert greater geopolitical power can exit the NPT at their will. Nonmember countries can then pursue a nuclear weapons program, as North Korea did in 2003. Doing so can result in international isolation or coercive action, such as sanctions or even covert attacks. However, some countries could feel so threatened that they are willing to risk those consequences. In these cases, major powers can ease a country’s fears by offering security assurances—commitments that they will not attack the country or will help defend it from attack. However, security assurances are typically contingent on denuclearization and the complete rejection of nuclear ambitions. For instance, the United States (a nuclear-armed country) maintains a so-called nuclear umbrella by providing its nonnuclear allies with binding defense guarantees. These security assurances reduce the incentive for nonnuclear U.S. allies to develop their own deterrents.

The combination of convincing countries they are safe without nuclear weapons and threatening penalties for those that pursue them has prompted numerous governments to abandon their nuclear programs. However, recent events could change that calculus. As harsh as the penalties are, no country has faced direct military action over its nuclear development. Moreover, several leaders have abandoned their nuclear programs only to come under threat later. Facing sanctions and international isolation, Iraq dismantled its nuclear program in the 1990s. A decade later, Saddam Hussein faced a U.S.-led invasion in 2003. Similarly, Libya agreed to disarm in 2003 and faced a civil war and a North Atlantic Treaty Organization–led–led intervention less than a decade later. Most recently in the news, Ukraine relinquished its sizable nuclear arsenal in 1994 in exchange for security assurances from the United States, Russia, and the United Kingdom. Those assurances were ineffective: in 2014 and 2022, Russia invaded Ukraine. The United States has provided significant aid to Ukraine with weapons and funds. However, U.S. support has stopped short of direct military intervention, in part over reluctance to enter conflict with a nuclear-armed Russia. The invasion underscores that nuclear-armed countries can act with a degree of impunity. Moreover, it shows that security assurances for nonnuclear countries are only as strong as their provider’s willingness and ability to follow through. Countries looking on could therefore conclude that they cannot trust outside assurances for their security. Nonnuclear countries might calculate that the penalties for developing a nuclear program are less costly than the risk of invasion.