Even political actors who disregard the international consensus against aggressive war may still fear the taboos surrounding the most powerful weapons.

Vladimir Putin does not play by the rules. The Russian president has long had a reputation for riding roughshod over the values of the international political community with uncompromising and macho disrespect. Analysts speak of the “Putin Doctrine”—a foreign policy of Russian dominance that is imposed regardless of widely accepted norms of state actor behavior. The Russian invasion of Ukraine is yet another example of Putin’s audacity. A NATO joint statement in March 2022 called the invasion “a fundamental challenge to the values and norms that have brought security and prosperity to all on the European continent.”

These broken norms include the violation of Ukraine’s sovereignty, an affront to the expectation that states should not invade other states without legitimate reason. Putin has also undercut the humanitarian rules of war. Russian forces have used controversial weapons, such as thermobaric devices and cluster bombs, and indiscriminately attacked civilian targets, including hospitals and a maternity ward.

Moreover, Putin has specifically threatened to violate taboos on the use of weapons of mass destruction (WMDs)—nuclear, biological, chemical, and radiological armaments. The concept of taboo comes from anthropology and refers to the cultural rejection of certain acts and objects as socially unacceptable—too unclean or too sacred to engage with. The concept has since been adopted within the discipline of international relations to explain the stigmatization of certain political actions and ideas on the basis that they are exceptionally disgusting and constitute an extreme threat.

Applying the concept of taboo to WMDs reflects the idea that these weapons are so abhorrent, so immoral, and so beyond the limits of toleration that any state that dares to use them will be rendered a pariah. International actors will not use, or in some cases even possess, these armaments—and will brand anyone who would use them as uncivilized and inherently wicked. Employing WMDs would incur extreme forms of sanction. We have already seen such a response in Syria, when the United States carried out air strikes against President Bashar al-Assad’s regime after its use of chemical weapons. Would Putin risk similar retaliation by violating the WMD taboo in Ukraine?

In her 2007 book The Nuclear Taboo, Nina Tannenwald argues that the nonuse of nuclear armaments since Hiroshima and Nagasaki is explained by the belief that these weapons are too awful to be employed. In that sense, Putin has technically not broken the nuclear taboo, yet his actions regarding Ukraine still put that taboo at stake.

Putin has repeatedly engaged in dangerous nuclear saber-rattling. He warned that any interference by third parties with the Russian invasion would elicit a response “such as you have never seen in your entire history.” The statement was interpreted as an explicit nuclear warning. Putin also threatened to transfer nuclear-capable missiles to Belarus, and his forces attacked the Chernobyl and Zaporizhzhia nuclear power facilities.

More recently, Putin has openly escalated his bellicose nuclear rhetoric, stating that he will use “all available means” to defend Russian territory—including the territory that Russia claims to have annexed from Ukraine. Speculation has risen that Putin is now prepared to use strategic or tactical nuclear warheads; US officials insist that the threat must be taken seriously. Putin’s belligerence may be aimed more at deterring NATO than setting up the actual use of nuclear arms. Yet he has disrupted the international order with his threats.

Failure to respect WMD norms also undermines future arms control diplomacy. WMDs are regulated by agreements that hold taboos at their core. These include measures such as the 1968 Nuclear Non-Proliferation Treaty (NPT), which seeks to eliminate all nuclear weapons stockpiles. Putin has effectively undermined the ideals that underpin pacts like the NPT, as well as the international community’s ability to negotiate extensions of such treaties or new ones. How can the United States and Russia, the two key players on global nonproliferation efforts, talk productively about reducing and eliminating arsenals when they are at each other’s throats on the nuclear issue in relation to Ukraine?

Even if Putin has not employed nuclear arms, there are concerns that he has in fact used chemical weapons—or wishes to. Richard Price discussed the illegitimacy of chemical weapons in his 1997 book The Chemical Weapons Taboo, arguing that they, too, are subject to a normative prohibition on their possession and use. It appears that Putin has violated this norm in Ukraine. It was reported in March 2022 that Russian forces had used white phosphorus in the eastern Donbas region. A month later it was claimed that a Russian drone had released an unknown chemical substance in Mariupol, poisoning three people. At the time of writing, these allegations are still being investigated.

Taboos remain a potent force within international relations.

Putin claims it is actually Ukraine that is willing to break this taboo and engage in chemical aggression. He has also alleged that Ukraine is developing biological weapons in laboratories funded by the United States. Joseph Manso, US ambassador to the Organisation for the Prohibition of Chemical Weapons, called Putin’s allegations “preposterous,” and White House press secretary Jen Psaki countered that Russia “has long maintained a biological program in violation of international law.”

Putin has been accused of preparing false flag claims, such as staging a WMD incident in order to create a pretext to justify the invasion of Ukraine or even a retaliatory WMD strike. His regime has a track record of accusing others of crimes that it intends to commit. And Putin has broken the chemical taboo in the past, as with the attempted assassinations of Sergei Skripal and Alexei Navalny using nerve agents, though Moscow denies responsibility.

Putin’s noncompliance can have implications beyond Ukraine. Yet we also need to treat this issue with caution. Putin either has not violated the WMD taboos, or it is not yet proved that he has done so—and even the strongest allegations against him are not at the level of mass destruction. The rules of the game have not been entirely overturned—even if he is only seeking, through limited compliance, to avoid the opprobrium and consequences that violating these taboos would incur.

We should not assume that Putin will never be motivated by the ideals of the international system, or that he cannot be controlled by them. Taboos and other international norms can still have at least partial influence even on an aggressor.

International norms can withstand challenges by actors like Putin if the rest of the world upholds them. Both NATO and US President Joe Biden have repeatedly warned that there would be “severe consequences” if Russian forces used WMDs in Ukraine. What the precise consequences would be was left unsaid. The lack of specificity may be a matter of strategic ambiguity. Yet US officials have alluded to more extreme sanctions, and have refused to rule out military options as well. Biden suggested that chemical warfare “would trigger a response in kind.” The international community is committed to a major response if Russia employs WMDs.

The commitment is not merely performative. Biden’s promise of a harsh response to WMD use is contrary to his broader reticence toward direct intervention in Ukraine. Seeking to avoid World War III, as he puts it, Biden has limited US involvement in the crisis to sanctions on Russia, humanitarian aid, and the provision of military assistance to Ukraine. Yet potential WMD taboo-breaking has been identified as a step too far—one that would demand more direct action. Polish President Andrzej Duda said in a March 2022 interview that WMD use by Russia would be “a game changer” for Western policy on Ukraine.

Despite Putin’s ingrained deviance from normative standards, taboos remain a potent force within international relations. Taboos are certainly not absolute, especially when they are challenged by a disruptive actor such as Putin. And if norms are not reinforced by the international community, they could fall apart.

Yet even Putin has not been entirely willing to undermine international values. He is clearly a threat to the global normative order, as the invasion of Ukraine demonstrates. But we should not dismiss the strength of that order, or assume that its rules cannot restrain the likes of Putin in the future. Taboos are deeply felt, instilling great fear in international actors. Their power cannot be ignored.