Ultimata feature as a core concept in the coercive diplomacy scholarship that emerged during the Cold War. Ultimata constitute strong coercive threats that consist of a specific demand from the opponent, a deadline for compliance, and the promise of violent punishment in case of non- compliance. Efforts in the coercive diplomacy scholarship to identify factors that favour compliance by the target of coercion have failed to produce a consensus on the utility of ultimata as a tool of coercive statecraft. The conventional wisdom holds that pursuing an ultimatum strategy is risky and that ultimata are prone to be rejected by their targets. This, however, is not borne out by the empirical record. Based on a newly compiled dataset of eighty-seven ultimata issued over the past century, the book argues that the conventional wisdom is misguided. Ultimata constitute dangerous bargaining moves, but still result in compliance in almost half of the cases. Absent compliance, ultimata typically lead to further escalation and armed confrontation. Yet, in case of escalation, in the majority of the cases coercers are likely to achieve their demands.

The book argues that the dearth of historical evidence considered in combination with the singular focus on compliance in the extant coercive diplomacy scholarship has obfuscated the purposes, the functions and the effects to which political leaders deploy ultimata. This has not served the scholarly understanding of threat behaviour in the interstate system. Political leaders issue ultimata for different purposes and to different effects across a variety of contexts. By implication, ultimata do not constitute a single-class phenomenon and should therefore not be assessed using a singular concept of utility.

This book makes three original contributions to the current state of knowledge concerning the use and utility of ultimata. First, the book provides an historical examination of how ultimata have featured in Western strategic, political and legal thought since Antiquity until the present, showing that ultimata have served a variety of purposes and have fulfilled multiple functions that have varied across strategic and historical contexts. The examination liberates the study of interstate threat behaviour from the shackles of the Cold War coercive diplomacy literature with its focus on coercive threats as being singularly aimed at compliance. Second, the book introduces a new, more comprehensive set of ultimata that includes eighty-seven cases issued in the period 1920-2020, and analyses trends and patterns in the use and utility of ultimata. The set is compiled on the basis of an extensive examination of conflict encyclopaedias, annual surveys of international relations, media archives, diplomatic history books, and specific conflict case studies. The set, that includes many cases that have thus far been ignored, provides a large evidentiary base that scholars of state threat behaviour can draw on. Third, the book offers a four- pronged typology on the basis of a structured focused comparison of the eighty-seven ultimata that explains the various purposes, functions and effects of ultimata: 1) the dictate, 2) the conditional war declaration, 3) the bluff, and 4) the brinkmanship ultimatum. The typology facilitates a better understanding of the various purposes to which decision makers issue unambiguous threats as well as the effects with which they tend to do so.

The insights offered in this book also have policy relevance against the background of the surge in interstate strategic competition and the increase in threat behaviour in recent years. A better understanding of the purposes and dynamics of interstate threat behaviour will help policymakers to prepare for challenges they are likely to face in the period to come.