In this book, Thomas Preston investigates the security implications of the spread of nuclear and biological weapons. He argues that their spread to weak state and nonstate actors will transform them from “lambs” into “lions” by giving them the ability to inflict massive damage on the United States and other major powers. At the same time, he argues that the spread of nuclear weapons to stronger states gives them the ability to deter attacks on their vital interests, and he develops a framework to assess the implications for crisis stability and international security. Preston argues that the spread of biological weapons to new state actors is also most likely to result in a spread of deterrent capability; however, because biological weapons lack the assured destructive capability of nuclear weapons and because of the norm against them, biological deterrence is likely to be opaque, existential, and less stable than nuclear deterrence (pp. 252–54). While he has great faith in the sensitivity of state leaders to the costs and risks of the use of nuclear and biological weapons (pp. 170, 254), he argues that terrorist groups are undeterrable and that terrorist possession of nuclear and/or biological weapons is the greatest threat posed by these weapons in today's world (p. 346).

Preston's effort to cover both nuclear and biological weapons is important. After all, states and other actors do not make decisions about the acquisition of particular weapons in a vacuum but face choices and trade-offs across different types of weapons. To the extent that both nuclear and biological weapons may serve as deterrent weapons for states, the effort to cover both is even more significant. In addition, the analytic frameworks that Preston presents for nuclear and biological weapons are an important attempt to identify and isolate the key factors that determine the impact of these weapons on international security, and will encourage other analysts to think carefully about the role of these factors in their own arguments. These are the real strengths of the book.

The book has weaknesses as well. First, in part perhaps because of his determination to view on the “world as it is,” Preston's focus is very much on the material characteristics of nuclear and biological weapons and the technological, material possibilities for their spread. However, while material reality may set constraints on what actors can do, it is rarely completely determinative of behavior. We need more attention paid to the motives and aims of actors and to strategic interaction if we are to understand how actors will choose to act within the material constraints that they face, and thus to understand the international politics of nuclear and biological weapons.

This is clear in his discussion of the spread of these weapons to both state and nonstate actors. Here, he largely leaves aside the question of motive, arguing that the critical question is the ability of actors to acquire these weapons, not their motivation to do so (pp. 17–18). There seems to be an underlying current of technological determinism here—if the technology is available, actors will acquire it. The problem is that this does not fit the empirical record. Many states that are capable of acquiring nuclear and biological weapons have decided to forgo them. This suggests that while some spread of these weapons may be inevitable, extensive spread may not be. In regard to nonstate actors, Preston briefly argues that the recent history of terrorist attacks, along with the rise of religiously motivated terrorism, demonstrates that terrorist use of nuclear and biological weapons is likely if terrorists are able to acquire them (pp. 230–33, 346). But the motivation of nonstate actors to undertake the costly, complicated, and risky effort to acquire nuclear and biological weapons has been challenged on various grounds, including the ability of these actors to launch more deadly and damaging attacks with other sorts of weapons (e.g., John V. Parachini, “Comparing the Motives and Outcomes of Mass Casualty Terrorism Involving Conventional and Unconventional Weapons,” Studies in Conflict and Terrorism 24 [September 2001]: 389–411).

Thus, more attention to motivation is necessary if we are to understand the potential spread of nuclear and biological weapons, and it is also necessary in order to evaluate the usefulness of particular nonproliferation policies. A case in point is the Nuclear Nonproliferation Treaty. While Preston largely dismisses it as a “hollow document” (p. 348), a more thorough investigation might reveal that the treaty has played an important role in keeping some nuclear-capable states from actually going nuclear.

In his analysis of the security implications of nuclear proliferation, Preston seeks to integrate the arguments of both the “proliferation pessimists” and the “proliferation optimists.” He argues that the impact of nuclear proliferation depends on three factors: their nuclear capabilities, the survivability of nuclear arsenals, and “the credibility of a state's deterrent threats to opposing decision makers” (p. 42). He attempts to classify different nuclear forces as providing varying degrees of deterrence ability, arguing for a distinction among a nascent or local deterrence ability, a regional deterrence ability, and a great power deterrence ability. He distinguishes among them on the basis of the differentiation and size of nuclear forces, the range and accuracy of delivery systems, and the interceptability of delivery systems (Table 2.1, pp. 44–45). But he confuses his own argument by contending here that different nuclear capabilities produce different deterrence capabilities, since he wants to argue that it is not just force structure but also the survivability of arsenals and the credibility of deterrent threats that are important (p. 42).

In addition, the significance of the qualitative changes in nuclear forces that Preston identifies is not clear. For example, he argues that North Korea has only a nascent nuclear force but that this force gives North Korea “substantial deterrent potential” (p. 110), and indeed even a potential North Korean nuclear capability seems to have constrained U.S. policy toward North Korea. But if a “nascent nuclear force” can provide deterrence for attacks on vital interests, the significance of the distinction between such a force, on the one hand, and a “regional” or “great power” force on the other, is unclear.

It may be that the different force structures identified by Preston result not in different deterrent capabilities but in different degrees of stability. As nuclear forces grow in size and survivability, preemption becomes even more difficult and crisis stability grows. But in order to make a compelling argument about stability, the author needs to address some of the issues at the heart of the disagreement between pessimists and optimists: How likely is it that new nuclear states will make the investments necessary to secure their nuclear forces? What is the right choice when faced with a trade-off between investment in securing one's nuclear forces or increasing their quantity and quality, and will states make that choice? Furthermore, he argues that both crisis stability and deterrent capability increase with increases in the size and complexity of forces. He thus implicitly rejects concerns about “normal accidents” and the arguments that “less is more” when it comes to new nuclear powers, but it is not clear on what basis he does so (on the risk of nuclear accidents, see Scott D. Sagan, The Limits of Safety, 1993; on why small nuclear forces might be better, see Jordan Seng, “Less is More: Command and Control Advantages of Minor Nuclear States,” Security. Studies 6 [Summer1997]: 50–92; see also David J. Karl, “Proliferation Pessimism and Emerging Nuclear Powers,” International Security 21 [Winter 1996/97]: 87–11).

From Lambs to Lions is a thought-provoking book that addresses one of the key issues in international security today: What are the implications of the spread of nuclear and biological weapons? Preston's efforts to analyze the potential spread of these weapons and the possible ways that state and nonstate actors will use them is valuable. But to fully understand the security implications of these developments, we need to understand more about the likelihood of the possibilities he outlines and what we can do to influence that likelihood.