Policy Brief - Belfer Center for Science and International Affairs, Harvard Kennedy School Quarterly Journal: International Security

Bolstering Nonproliferation through Disarmament Progress

  • Jeffrey W. Knopf
| March 2013

This policy brief is based on "Nuclear Disarmament and Nonproliferation: Examining the Linkage Argument," which appears in the winter 2012/13 issue of International Security.



  • Nuclear Weapon States Have Not Fully Lived Up to Their Disarmament Pledges. In Article 6 of the Nuclear Nonproliferation Treaty (NPT), the five nuclear-armed states recognized by the treaty pledged "good faith" efforts to achieve nuclear disarmament. Although the United States and Russia have made significant nuclear arms reductions since the height of the Cold War, many nonnuclear weapon states have expressed dissatisfaction with what they perceive to be unwillingness among the nuclear weapon states to eliminate their nuclear arms.
  • Commitment to Nuclear Abolition Would Strengthen the Nonproliferation Regime. Experts vigorously debate whether movement toward nuclear disarmament decreases the likelihood of further nuclear proliferation. An analysis of the arguments both for and against this "linkage hypothesis" shows that, on balance, signs of commitment to nuclear disarmament by the nuclear weapon states will tend to enhance support for nonproliferation. Because many other factors affect state decisionmaking, however, progress on nuclear disarmament will not by itself guarantee a more effective nonproliferation regime.
  • Implementing the 2000 NPT Review Conference's Thirteen Steps Would Demonstrate Seriousness about Disarmament Pledges. U.S. officials have suggested that nuclear arms reductions demonstrate U.S. compliance with Article 6. Nonnuclear weapon states, however, do not focus on absolute numbers of weapons. They instead look for policy decisions that demonstrate a willingness to reduce reliance on nuclear weapons. Efforts to complete implementation of the thirteen "practical steps" agreed to at the 2000 NPT Review Conference would signal that nuclear weapon states are serious about their Article 6 obligations. U.S. Senate ratification of the Comprehensive Nuclear Test Ban Treaty (CTBT) would be an especially strong signal of U.S. interest in creating the conditions needed for a nuclear weapon–free world.


Article 6 of the Nuclear Nonproliferation Treaty calls for good-faith negotiations to eliminate nuclear weapons. This requirement in the treaty has led some commentators to suggest that, unless the NPT-recognized nuclear weapon states are perceived to be committed to disarmament, the nonproliferation regime will unravel. Others, in contrast, contend that nuclear weapon state actions on disarmament have no bearing on the factors that could lead to the further spread of nuclear weapons.

In evaluating the possible connection between disarmament and nonproliferation, it is important to consider both direct and indirect linkages. In direct linkages, nuclear weapon state actions or postures directly trigger proliferation by others. Indirect linkages could arise if a failure by nuclear weapon states to fulfill their disarmament obligations leads nonnuclear weapon states to refuse to cooperate to enforce nonproliferation, thereby lessening the barriers to proliferation.

Counterarguments also come in two variants. In most cases, critics claim there simply is no linkage. They argue that other factors drive proliferation instead, rendering nuclear weapon state actions on disarmament irrelevant. Some critics even predict a reverse linkage. They express concern that movement toward nuclear disarmament, especially by the United States, will weaken security guarantees to nonnuclear weapon allies, making those states more likely to seek a nuclear deterrent of their own.

An analysis of the arguments on both sides of the linkage debate suggests, however, that signs of commitment to nuclear disarmament by the nuclear weapon states will, on balance, tend to enhance support for nonproliferation.


Critics of the linkage argument argue that the United States and Russia have cut their nuclear arsenals substantially without any noticeable subsequent increase in support for nonproliferation. Nonnuclear weapon states, however, tend not to view nuclear arms reductions as the best indicator of compliance with Article 6; they attach greater weight to policies that convey an intent among weapon states to keep nuclear weapons indefinitely. As a result, even if there is no correlation between previous stockpile reductions and nonproliferation (a point that has not yet been proven), this is not the only relevant evidence for assessing the linkage hypothesis. Specifying different causal logics that might lead to a connection, or lack of connection, between disarmament efforts and nonproliferation can help determine other relevant empirical tests.

Five Potential Sources of Linkage: Five factors are likely to be relevant in determining whether there is a link between disarmament and nonproliferation: (1) states' security calculations; (2) the institutional features of the nonproliferation regime and associated bargaining dynamics; (3) norms associated with nuclear weapons; (4) domestic politics; and (5) human psychology and its impact on individual decisionmaking. Within each of these five factors, it is possible to identify several ways that nuclear weapon state behavior could influence nonnuclear state actions or, alternatively, account for a lack of linkage. This policy brief does not list all the potential causal pathways that can be identified, but instead summarizes the results of examining the full list.

No Dominant Logic: In general, arguments for and against the linkage hypothesis illustrate the limitations on the other perspective, suggesting that neither is universally applicable. This has an important logical implication: even if the expectation of "no linkage" is true sometimes, it will not apply in all cases. This means that some degree of linkage likely exists, but of varying strength depending on circumstances.

Take, for example, arguments about security. One version of the no linkage position holds that proliferation is driven mainly by regional security concerns: if potential proliferators are focused on regional rivals rather than on the NPT nuclear weapon states, then nuclear weapon state policies with regard to disarmament will not factor into their calculations. Yet, in some cases, the regional rival of concern might be a nuclear weapon state. Indian elites, for example, often cite China's nuclear weapons program as a reason why India needed the bomb. Hence, security arguments do not preclude the possibility of a linkage. Instead, security considerations could make the extent of movement toward nuclear abolition largely irrelevant to some states, but highly relevant to others.

Fairness Concerns: The most potent reason to expect a linkage between nonproliferation and disarmament involves an argument based on norms and psychology. Nonnuclear states contend that they are being asked to take on new obligations—such as the Additional Protocol to NPT safeguards agreements, or restrictions on developing the nuclear fuel cycle—at a time when nuclear states have not fulfilled their end of the original NPT bargain. Research shows that perceptions of unfair or unequal treatment—such as might arise when one party violates a norm or a previous bargain—can lead to strong emotional responses. These could lead some nonnuclear states to withhold cooperation to strengthen or enforce the NPT, even though it would not be in their interests to see other states acquire nuclear weapons.


On balance, signals of nuclear weapon state commitment to nuclear abolition should help strengthen the nonproliferation regime. It is not up to U.S. officials, however, to tell nonnuclear weapon states what counts as such a signal. These states have made it clear that they care more about policies indicating a commitment to an eventual global zero than they do about nuclear arms reductions since the Cold War. Nuclear weapon states need to listen and respond to nonnuclear states' views about actions that would demonstrate compliance with Article 6.

One agreed-upon checklist already exists. At the 2000 NPT Review Conference, states approved thirteen "practical steps" meant to advance implementation of Article 6. Action has been taken on some steps, but on others progress has been incomplete or even nonexistent. For the United States, Senate ratification of the CTBT would be a powerful symbol of U.S. support for the thirteen practical steps and commitment to Article 6.

At the same time, one should not expect too much from action on nuclear disarmament. There are many factors that affect both state decisions about whether to seek nuclear weapons and the strength of the nonproliferation regime. Because of these other factors, greater movement on disarmament will not address all of the weak points in global nonproliferation efforts. It is also important to keep in mind the possible perverse effects of nuclear arms reductions, should these reductions lead to a weakening of U.S. security assurances to key allies. A research project that I led on security assurances found that recipients tend not to focus on the size of the U.S. arsenal, but to instead judge the credibility of assurances based on the quality of their relationship with the United States, the extent of defense cooperation, and the existence of channels for consultation with Washington. If the United States is willing to listen to its allies, while also taking into account the views of nonaligned states, it should be able to continue reducing the nuclear arsenal without setting off a new round of proliferation. In sum, although the impact is likely to be modest, a reinvigorated commitment by the NPT nuclear weapon states to work toward global zero should bolster nonproliferation efforts.


Choubey, Deepti. "Are New Nuclear Bargains Attainable?" Washington, D.C.: Carnegie Endowment for International Peace, October 2008.

Ford, Christopher. "Nuclear Disarmament, Nonproliferation, and the 'Credibility Thesis.'" Briefing Paper, Washington, D.C.: Hudson Institute, September 2009.

Joyner, Daniel H. Interpreting the Nuclear Non-Proliferation Treaty. New York: Oxford University Press, 2011.

Knopf, Jeffrey W., ed. Security Assurances and Nuclear Nonproliferation. Stanford, Calif.: Stanford University Press, 2012.

Ogilvie-White, Tanya, and David Santoro. "Disarmament and Non-Proliferation: Toward More Realistic Bargains." Survival 53, no. 3 (June/July 2011): 101–118.

Sagan, Scott D., and Jane Vaynman, eds. "Arms, Disarmament, and Influence: International Responses to the 2010 Nuclear Posture Review." Special issue, Nonproliferation Review 18, no. 1 (March 2011): 17–262.

Trachtenberg, David J. "U.S. Extended Deterrence: How Much Strategic Force Is Too Little?" Strategic Studies Quarterly 6, no. 2 (Summer 2012): 62–92.



Jeffrey W. Knopf is a professor in the Graduate School of International Policy and Management, program chair of the Nonproliferation and Terrorism Studies program, and a senior research associate with the Center for Nonproliferation Studies at the Monterey Institute of International Studies.


Statements and views expressed in this policy brief are solely those of the authors and do not imply endorsement by Harvard University, the Harvard Kennedy School, or the Belfer Center for Science and International Affairs.

For more information on this publication: Please contact International Security
For Academic Citation: Knopf, Jeffrey W.. “Bolstering Nonproliferation through Disarmament Progress.” Policy Brief, Quarterly Journal: International Security, Belfer Center for Science and International Affairs, Harvard Kennedy School, March 2013.

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