International Law

Revisiting the Treaty on the Prohibition of Nuclear Weapons

By Shanelle Van
Tuesday, November 27, 2018, 9:32 AM

One year ago, the International Campaign to Abolish Nuclear Weapons won the Nobel Peace Prize for its advocacy that contributed to the first legally binding treaty ban of nuclear weapons: the Treaty on the Prohibition of Nuclear Weapons, also known as the nuclear ban treaty. If and when it enters into force, the TPNW will legally bar treaty parties from—among other prohibited activities—possessing, developing, acquiring, testing, stockpiling, transferring, stationing, or threatening the use of nuclear weapons. It will also be illegal for treaty parties to “assist, encourage or induce, in any way, anyone to engage in any activity prohibited” by the treaty.

The treaty’s supporters acknowledge that the agreement will not, realistically, cause the immediate disarmament of nuclear-armed states, which boycotted the negotiations and are unlikely to join the treaty. But that is not the advocates’ aim. The primary purpose of the treaty, they offer, is to declare nuclear weapons illegal and thereby chip away at the legitimacy of possessing them—in the hopes that, if norms shift against nuclear weapons, even nuclear-armed states not party to the treaty will eventually be pressured into disarming. This post explains the controversy surrounding the negotiations of the treaty, the debate over its substance, and its uncertain future in creating legal change.


The Treaty on the Prohibition of Nuclear Weapons was born primarily of frustration amongst some states and nongovernmental activists with a disarmament framework that has for the past half-century revolved around the Nuclear Non-Proliferation Treaty (NPT). Since opening for signature in 1968, the NPT has provided the “grand bargain” underlying the nuclear nonproliferation regime: Countries without nuclear weapons would not develop or acquire them, and those with nuclear weapons would “pursue negotiations in good faith on effective measures” toward nuclear disarmament. Through the multilateral NPT, and through bilateral agreements between Russia and the United States, the number of nuclear weapons worldwide has been reduced dramatically—from over 70,000 weapons in the 1980s to an estimated 14,485 by mid-2018.

But the decline has slowed, and a perceived shift in the United States’ nuclear policy in the early 2000s spurred the sentiment that NPT nuclear-weapon states had not held up their end of the bargain. In recent years, disarmament advocates have pointed to nuclear-armed states’ plans for modernizing their nuclear arsenals as further evidence of their intention to retain those weapons for at least the next few decades. The Congressional Budget Office estimated that the Obama administration’s modernization plans, as outlined in its 2017 budget request, would cost $1.2 trillion over the subsequent 30 years. Other NPT nuclear-weapon states, including Russia, the United Kingdom, and France, have similarly started down the path of modernizing their respective arsenals. For disarmament groups, the cumulative effect of these modernization plans, taken together with past instances in which states failed to reach consensus through established NPT processes, has been to demonstrate that the NPT is not enough. Disarmament advocates believed that, despite the NPT’s “good faith” obligations, there was a “legal gap” that needed to be filled: Nuclear weapons, like chemical and biological weapons, needed to be banned.

In December 2016, the U.N. General Assembly passed a resolution that called for negotiations on a nuclear ban treaty to take place over two sessions: March 27–31 and June 15 through July 7, 2017. As those negotiations began, however, none of the nine countries known or believed to have nuclear weapons—the five recognized NPT nuclear-weapon states (the United States, the United Kingdom, France, China, and Russia), plus India, Pakistan, Israel, and North Korea—participated in the talks. Neither did numerous states without nuclear weapons, including allies of the United States such as the NATO member states (except the Netherlands), South Korea, Canada, Australia, and Japan.

Opponents of the negotiations advanced three primary criticisms. First, the concept of a ban ignored the reality that the current international security environment continued to make deterrence necessary. Any ban treaty would rush to the finish line of disarmament, without first addressing the security threats that motivate states to possess nuclear weapons in the first place. Second, the pressure campaign could only succeed in democratic countries responsive to protest and normative arguments, not in authoritarian states like North Korea, which would ignore the calls for disarmament. In former U.S. Ambassador to the U.N. Nikki Haley’s words, a nuclear ban would “allow[] the bad actors to have them and those of us that are good, trying to keep peace and safety, not to have them.” Third, a ban treaty would, at best, divert finite attention and resources away from established nuclear security and disarmament mechanisms. At worst, experts cautioned, a treaty that did not explicitly affirm NPT obligations might even undermine the existing NPT framework.

Formal negotiations took place over a mere four weeks. On July 7, 2017, 122 states voted to approve the final text of the Treaty on the Prohibition of Nuclear Weapons. Just one state, the Netherlands, voted against adoption, and one, Singapore, abstained.

The Treaty’s Merit: Arguments For and Against

Those who opposed the negotiations have remained largely unswayed after seeing the treaty’s final text, noting several substantive issues. Among other potential problems, the treaty does not define its terms, leaving open questions about the legal obligations it creates (for example, what it means to “assist, encourage or induce” in contravention of the treaty) that the treaty’s supporters have recently tried to answer. It also does not foreclose the possibility of tension with the NPT: Legal experts have read the nuclear ban treaty to “subordinate” the NPT to it. Further, experts argue that the treaty sets forth insufficient disarmament verification standards. For example, it does not detail how a “competent international authority,” which has yet to be designated, would verify the elimination of a nuclear weapons program should a nuclear-armed state seek to join the treaty in the future. It also, Newell Highsmith and Mallory Stewart contend, creates a discriminatory framework that would effectively keep any nuclear-armed state from joining the treaty. Assistant Secretary for International Security and Nonproliferation Christopher Ford, who was the senior director for nonproliferation on the National Security Council at the time, decried the treaty in 2017 as “entirely unserious about real disarmament.”

John Carlson has questioned whether some of these shortcomings might have been ironed out had drafters negotiated the treaty over a longer period. As Gaukhar Mukhatzhanova recounted, some delegations had substantive concerns that remained unresolved due to the speed of the negotiations. For example, states disagreed as to the activities that the term “test” would encompass. Some states also asserted that they would consider the prohibition on “assist[ing], encourag[ing] or induc[ing]” to bar the transit of nuclear weapons, though “transit” was deliberately left out of the treaty text. Nonetheless, there was a “prevailing desire” in the room to reach a final text by July 7, possibly due to the worry that political will would wane if an extension became necessary.

Treaty supporters such as Beatrice Fihn, the Executive Director of International Campaign to Abolish Nuclear Weapons, say that the criticisms are either incorrect or overblown. First, proponents have argued that some preceding disarmament treaties do not contain definitions either, and the nuclear ban treaty’s legal requirements can be understood because the treaty’s terms are used elsewhere in international law. Second, since the treaty is intended to go further than the NPT in its prohibitions, it would be counterproductive, according to Fihn, to allow the NPT to “override” the nuclear ban treaty. Third, Fihn contends that, while the TPNW does not raise the safeguards requirements, “this treaty does not lower the standard of safeguards from the NPT.” Importantly, from the perspective of the treaty’s advocates, it has also already begun changing conversations about nuclear weapons even before entering into force. Some countries that do not possess nuclear weapons but rely on the United States’ nuclear guarantees felt compelled to explain to their constituents why they were boycotting the treaty negotiations. Advocates remain confident that the treaty will shake up the “nuclear weapons establishment.”

Slow Rate of Ratification

While outward support for the treaty has not dimmed one year on, that support is not yet reflected in the treaty’s signatures and ratifications. The treaty has to date collected 69 signatories and 19 ratifiers—with four of the most recent ratifications deposited on Sept. 26. When Fihn was asked this past summer—at the time, the treaty had only 10 ratifiers—why more states were not formally joining the treaty, she defended the pace in part by citing the paces of comparable treaties. “It’s faster than any other nuclear weapons treaty so far,” she said. “It took the Comprehensive Nuclear Test Ban Treaty more than a year before it got the second ratification. It’s faster than the NPT, it’s faster than the Chemical Weapons Convention. It’s completely on pace in terms of other treaties.”

This is partially true now—though the treaty currently falls toward the slower end of the pack when compared to several other disarmament treaties in terms of pace toward ratification. (See figure below.) As of Nov. 12,  or 418 days after opening for signature, the treaty had attained 19  of the 50 ratifications necessary for entering into force. That rate is apace with the NPT and quicker than the Chemical Weapons Convention when those treaties were 418 days old. Other disarmament treaties have, however, proceeded more quickly than the nuclear ban treaty. Those treaties include the Biological Weapons Convention, as well as the Mine Ban Treaty (often cited by nuclear ban proponents as a model for civil society leading the way in treaty negotiations and changing norms around specific weapons), the Convention on Cluster Munitions, and the Arms Trade Treaty.


Date opened for signature

418 days post-opening for signature

Percent of ratifications necessary for entry into force attained 418 days post-signature opening

Date of entry into force

Chemical Weapons Convention

Jan. 13, 1993

March 7, 1994

6 percent (4/65)

April 29, 1997, 180 days after the date of deposit of 65th instrument of ratification, but no earlier than two years after opening for signature

Treaty on the Prohibition of Nuclear Weapons

Sept. 20, 2017

Nov. 12, 2018

38 percent (19/50)


Nuclear Non-Proliferation Treaty

July 1, 1968

Aug. 23, 1969

42 percent (18/43)

March 5, 1970, after ratification by 43 states (the United States, United Kingdom, and Soviet Union required) and deposit of their instruments of ratification

Arms Trade Treaty

June 3, 2013

July 26, 2014

82 percent (41/50)

Dec. 24, 2014, 90 days following date of deposit of 50th instrument of ratification

Biological Weapons Convention

April 10, 1972

June 2, 1973

86 percent (19/22)

March 26, 1975, after deposit of instruments of ratification by 22 states (the United States, United Kingdom, and Soviet Union required)

Convention on Cluster Munitions

Dec. 3, 2008

Jan. 25, 2010

90 percent (27/30)

Aug. 1, 2010, on first day of sixth month after month in which 30th instrument of ratification was deposited

Mine Ban Treaty

Dec. 3, 1997

Jan. 25, 1999

150 percent (60/40)

March 1, 1999, on the first day of the sixth month after month in which 40th instrument of ratification was deposited


Proponents and critics have offered differing explanations for the TPNW’s rate of ratification. In an interview, Fihn said, “[P]arliaments don’t work that fast. Ask the United States how fast it ratifies treaties … For some countries, though, the issue is simply that there was quite a short time between treaty adoption and the signing ceremony. What we heard from a lot of smaller states, particularly in Africa, is that they just did not have time to put it through their internal mechanisms. And as soon as the signing ceremony was over they sort of put it on a shelf.” Recently, she also predicted that the treaty could enter into force by the end of next year, as “[w]e have about 25, 30 countries that say that they will be ready by the end of 2019.” John Carlson, on the other hand, has theorized that states that voted to approve the treaty text may now be “hesitant, perhaps because of greater awareness of the problems with the treaty.” Christopher Ford has similarly questioned whether the treaty proponents would succeed in convincing states to join:

Supporters of the ‘Ban’ effort seem to be struggling a bit to persuade states that it would really be in their interest to sign up, and while they may still eventually get enough accessions to meet the requirements TPNW’s entry-into-force provisions, a number of countries seem to be gradually waking up to the potential real-world costs and risks of joining.

Some combination of these factors might be at work. On the one hand, there are states, such as Brazil and Ireland, that have begun but not yet completed their internal legislative processes. On the other, some states, after voting to approve the treaty text, indicated a hesitation to join the treaty until they conducted a deeper assessment of the treaty’s implications. As Alicia Sanders-Zakre noted at the time, the Marshall Islands, Sweden, and Switzerland voted to approve the treaty text, but their representatives played down the meaning of those votes afterwards, saying that the states needed to consider the treaty’s legal implications. The representative of Sweden explained that her country voted in favor of adoption “[d]espite the complexity of the matter, and the unprecedentedly limited time at [Sweden’s] disposal.” She highlighted that there were a number of “crucial elements of this treaty that [did] not meet what [Sweden’s] delegation was aiming for,” including specific language within the text with which Sweden disagreed. A number of the countries that commissioned studies analyzing the treaty have only recently concluded those efforts (the foreign ministries of Norway and Switzerland each recommended against ratification). As such, some states may still be determining what legal obligations the nuclear ban treaty entails and whether compliance with the treaty can be reconciled with those states’ other obligations, activities, and interests. The fact that the Marshall Islands, a vocal opponent of nuclear weapons, has yet to sign or ratify the treaty demonstrates just how difficult those concerns may be to untangle.

Uncertain Legal Implications

When supporters opted to finalize the treaty text after only four weeks of formal negotiations, they implicitly decided that they would make the most of the political momentum, even if that might come at a cost of greater consensus and clarity. Whether or not that gamble will pay off has yet to be determined. Though the United States, United Kingdom, France, China, and Russia have jointly declared that they will not join the treaty, this comes as no surprise to the treaty’s advocates, who claim that the document enjoys the support of many other states. Some of those other states may indeed prefer the nature of the treaty—not detailed in its requirements, but strong in its condemnation of nuclear weapons and the status quo. Moreover, the treaty’s broadly drawn legal obligations may, whether or not by design, enable disarmament advocates to argue that the treaty prohibitions encompass a wider swath of activities.

The danger in the gamble will materialize, however, if the treaty’s substantive weaknesses—partially a result of its accelerated drafting process—undermine the clarity of its legal obligations and its prospects for ratification. That may, in turn, have the inadvertent consequence of diminishing the treaty’s future legal effect when disarmament advocates later seek to revisit the question of nuclear weapons’ legality. As Highsmith and Stewart have explained, the treaty is unlikely to establish the illegality of nuclear weapons as a matter of customary international law. But it may well become harder for disarmament advocates to demonstrate that state practice and opinio juris align with treaty principles, such that those principles pass into customary international law, if states manifest different interpretations of what the treaty means and the text is itself unclear in its prohibitions. Further, the number of treaty ratifications will likely matter: As the International Court of Justice has suggested in the North Sea Continental Shelf Cases, even a “respectable” but low number of ratifications might be insufficient to reinforce any future arguments that disarmament advocates would make regarding customary international law.

Whether or not the Treaty on the Prohibition of Nuclear Weapons has the normative and legal effect its supporters intend, it will be the elephant in the room for nuclear policy discussions to come.