Whether in laconic tweets or loquacious orations, world leaders spend an awful lot of time communicating, both to us and to one another. Yet although decision makers are rarely at a loss for words, international relations scholars have often had difficulty explaining how rhetoric matters in international disputes, especially when operating out of a rational choice tradition that views talk as cheap. In Statements of Resolve, Roseanne McManus shows categorically that words matter in international politics, making this book a must-read for anyone interested in communication and the domestic politics of international bargaining.

The logic of McManus’s argument is straightforward: Leaders who talk tough by issuing “statements of resolve” achieve more favorable outcomes in foreign policy disputes. Because resolve itself is unobservable, foreign decision makers are forced to infer it from verbal statements, and these words will have the most force when leaders have the ability to follow through on them. Teddy Roosevelt had it wrong: Leaders should both speak loudly and carry a big stick.

As McManus notes, the notion that threats are more effective when they are credible is not a counterintuitive argument (p. 2), and so the book’s central contribution is to carefully stipulate the conditions in which states have the ability to follow through on resolved statements in the first place: when their relative military capabilities are high, when the relevant domestic veto players are hawkish, and when their leaders are more secure in office. Although these claims may seem uncontroversial, they also put McManus in stark opposition to many of the workhorse models in the domestic politics of IR, which often focus on domestic veto players’ political interests rather than their policy preferences, argue that leaders that are insulated from public punishment should make less credible threats, and posit that insecure leaders should be more likely to “gamble for resurrection” (see, e.g., Kenneth Schultz, “Domestic Opposition and Signaling in International Crises,” American Political Science Review 92 [1998]; James D. Fearon, “Domestic Political Audiences and the Escalation of International Disputes,” American Political Science Review 88 [1994]; George W. Downs and David M. Rocke, “Conflict, Agency, and Gambling for Resurrection: The Principal-Agent Problem Goes to War,” American Journal of Political Science 38 [1994)]).

Above all else, Statements of Resolve reminds us why books matter: The strength of the work comes from McManus’s careful and ambitious multimethod approach, motivating her theory with a series of formal models before marshaling an impressive diversity of evidence—content analysis, large-n statistical analysis, event data, detailed Cold War case studies—in support of her claims, a kind of methodological fusillade that is extraordinarily difficult to fit into steadily shrinking journal articles. The most notable part of this barrage is the original data set of U.S. presidents’ resolved statements in five rivalries from 1975 to 2000, and all militarized interstate disputes (MIDs) involving the United States between 1950 and 2010, scored using an original dictionary of resolved words and phrases (p. 50), a creative and highly valuable resource that IR scholars will turn to for years to come.

The question of how resolved statements shape dispute outcomes is a crucially important one—and like most of the other important questions in IR, is also incredibly difficult to answer. To her credit, McManus is precise and careful in her analysis, performing a heroic number of robustness checks. Nonetheless, it is worth noting just how difficult a question it is.

McManus’s theory is not that resolve wins wars, but that expressing it verbally does. If leaders are strategic in what they say and when, identifying the effects of resolved statements on dispute outcomes requires controlling for any unobserved confounds that could be responsible for both. If leaders issue resolved statements because they are resolved, for example, and resolve shapes how actors otherwise conduct themselves in disputes, it is difficult to know how much of the work is being done by the statements themselves.

The point also raises interesting questions about foreign policy substitutability. Public verbal statements are one way to signal resolve, but leaders can also turn to deeds rather than words—either in the form of costly signals before conflicts begin or events on the battlefield once fighting takes place—and the MID data the study uses as its backbone is insufficiently granular to disentangle bark from bite. Although McManus’s critique of experimental methods is well taken, experiments are well suited to disentangling some of these thorny questions about causally identifying the effects of speech, a promising area for future research.

The book studies resolved statements through a rational choice approach, building on canonical bargaining models of war. In many ways, this is one of the book’s strengths, making it a successor to Anne Sartori’s pioneering work, Deterrence by Diplomacy (2005). Yet McManus’s findings also subvert this tradition. For example, although the book has “coercive credibility” in its subtitle, and makes repeated reference to actors’ “ability to follow through” (e.g., p. 19), this book is not about coercion or credibility as usually understood in IR, since the resolved statements she studies are not limited to threats. (Indeed, there are questions as to how suitable the MID data are for studying threats in the first place; on this score, see Alexander Downes and Todd Sechser, “The Illusion of Democratic Credibility,” International Organization 66 [2012]). One of the book’s most fascinating findings is that “negative characterizations” (e.g., calling an opponent an “evil empire”; unfortunately, “little rocket man” and “dotard” are outside the time span of this study) seem to be nearly as effective as explicit threats, and maybe more effective than concrete demands and refusals (pp. 85–86). It is not clear how well traditional bargaining frameworks, which are narrowly focused on threats, capture this dynamic.

This insult comedy of great power politics, then, suggests potentially fruitful connections between McManus’s work and research on diplomacy, discourse, and rhetorical action from outside the confines of rational choice (e.g., Frank Schimmelfennig, “The Community Trap: Liberal Norms, Rhetorical Action, and the Eastern Enlargement of the European Union,” International Organization 55 [2001]; Stacie E. Goddard and Ronald R. Krebs, “Rhetoric, Legitimation, and Grand Strategy,” Security Studies 24 [2015]). Thinking about resolved statements from these alternative perspectives is helpful on a number of counts.

First, it reminds us that discourse is inherently social. McManus makes an important contribution in focusing on the statements of U.S. presidents; future work might study resolve polyphonically by also incorporating the “fighting words” used by other political officials as well. The case studies show that resolved statements are more effective when presidents’ words are backed up by prominent hawkish voices in Congress, for example, but presumably, foreign observers are inferring the hawkishness of potential veto players based on the extent to which they too are issuing statements of resolve. Future work might also consider studying resolved words not as a monologue but as a dialogue, modeling these statements as part of a broader conversation between actors in a dispute. This not only raises interesting theoretical questions about spillover effects—to what extent do third parties draw inferences about resolve based on public statements directed at other actors?—but also coding questions. One of the many striking findings in the book is that, over time, U.S. presidents have become increasingly likely to use resolved language in crises. Since, however, the coding scheme was generated from the perspective of the present (reading presidential statements, and looking for words and phrases that read as resolved), one might imagine that its validity would decrease the more foreign the discursive context—a question about temporal distance that also has implications for social distance.

Second, what role do emotions play in statements of resolve? Scholars of diplomacy have recently focused on the role of face-to-face diplomacy in harnessing affective or physiological mechanisms in order to credibly convey intentions (Marcus Holmes, “Mirror Neurons and the Problem of Intentions,” International Organization 67 [2013]; Seanon S. Wong, “Emotions and the Communication of Intentions in Face-to-Face Diplomacy,” European Journal of International Relations 22 [2016]), but emotions have an important signaling value even at a distance, and many of the resolved words or phrases in McManus’s dictionary and cases are affectively charged. Anger seems particularly pertinent. Psychologists have found that participants who express anger perform better in negotiations—nicely paralleling McManus’s findings—and recalibrational models of anger in evolutionary biology suggest that anger evolved precisely for its bargaining advantages (Gerben A. van Kleef, Carsten K. W. De Dreu, and Antony S. R. Manstead, “The Interpersonal Effects of Anger and Happiness in Negotiations,” Journal of Personality and Social Psychology 86 [2004]; Aaron N. Sell, “The Recalibrational Theory and Violent Anger,” Aggression and Violent Behavior 16 [2011]). Emotions thus offer an alternative set of causal mechanisms beyond those emphasized in conventional bargaining models.

Finally, the book is especially relevant in the era of Donald Trump, who ran for the presidency on a foreign policy platform that was low in details but high in volume, a swashbuckling streak of “fire and fury” he has since continued in office, to the acclaim of his supporters and dismay of his opponents. McManus’s main finding—that good things come to those who bait—is remarkably consistent with the Trumpian ethos, and the contextual factors that she finds enhance the efficacy of resolved statements all seem to at least currently be in Trump’s favor. American military primacy persists, and Trump seeks to increase military spending further. As of this writing, the Republicans control both the House and Senate and do not show particular signs of dovishness. Trump’s net public approval is low, but his approval among his supporters (the segment of the public he cares about the most, and whose fervor keeps the rest of the Republican Party at bay) remains strong. If McManus’s theory is correct, we should expect that Trump’s foreign policy should perhaps be more successful than many political scientists surmise. In these, and so many other ways, McManus’s meticulous study offers us much valuable food for thought.