Well before the 9/11 attacks, scholars and policy makers alike concluded that terrorist violence had undergone an important transformation in the last quarter of the twentieth century. Unlike the terrorist campaigns that took place immediately following the Second World War, which were largely conducted by separatists and ideologues against erstwhile imperial states weakened by war and decolonization, the "new terrorism" appeared to center on the preservation of traditional religious values in the face of modernization. This shift in focus was ostensibly accompanied by marked changes in both scope and lethality, with "new" terrorists focusing primarily on targets in other countries and seeking to maximize body counts. But has the "new" international terrorism fully overshadowed or supplanted the "old" domestic variety? Just as importantly, even if we have seen the end of an era, what general conclusions can be drawn about the impetuses and conduct of domestic terrorism in its "golden age"? In this crossnational study of postwar Western European terrorism, Jan Oskar Engene has both provided clear (and sometimes surprising) answers to the above questions and compiled a new and invaluable database for scholars wishing to extend this line of inquiry.

Engene begins by delineating a "communicative" theory of domestic terrorism that centers on the relationships among four major actors: terrorists, the immediate targets of their violence, and the two groups to whom they wish to convey political messages with that violence, the state and the public. According to Engene, terrorist violence diminishes the legitimacy of the state's rule by breaking its monopoly on the use of force and, where legitimacy is based on legality and the rule of law, by forcing the state to change the rules that govern its relationship to the public (e.g., by infringing upon established civil liberties in an effort to conduct counterterrorism). If legitimacy can be sufficiently eroded, the foundation is laid "for a change of allegiances and loyalties between groups in society." (p. 27) When terrorists wish to force the state to accede to their substantive political demands (as is the case with separatists or Left-wing ideologues), they attempt to follow up the diminution of public loyalty to the state with the establishment of bonds between themselves and the public based in part on popular identification with their goals. When terrorists wish instead to delegitimize the rule of law (as is the case with Right-wing ideologues), they seek to replace public loyalty to the legalist state with a "subordinate" relationship in which legitimacy is predicated on power or force, while at the same time strengthening their own relationship to that increasingly authoritarian government. As such, Engene portrays "anti-state" and "pro-state" domestic terrorism as differing not in the methods by which each hopes to force change, but in how each applies those methods to disrupt and construct bonds of loyalty among political actors.

In the legalist Western European context, Engene posits that domestic terrorism is more likely when a particular government has experienced one or more of three types of problems in the process by which they developed legitimacy. First, problems of ethnic fractionalization are likely to lead to separatist movements, especially given Western Europe's self-deterministic state building tradition. Second, problems of integration that result in the de facto exclusion of one or more sectors of society from the political process (such as fringe parties) will lead those excluded to use violence in lieu of a political voice. Finally, problems of continuity, characterized by "ruptures" in the democratic development process, can lead to violence on the part of groups that long for the stability and glory (real or imagined) of past, non-legalistic governments. By polarizing societies and thus providing a vehicle by which support for the terrorist's cause can be mobilized, such preconditions cast doubt on the true legitimacy of the state, giving terrorists an "in" to further weaken that legitimacy through their communicative violence. Engene arrives at a more comprehensive predictive theory of terrorism by adding these factors to features of modern societies (the level of democracy, modernization, social injustice, and post-industrialism) identified by previous studies as facilitators of terrorist violence.

Engene tests his hypotheses against his self-developed Terrorism in Western Europe: Event Data (TWEED) dataset, a comprehensive, longitudinal compilation of domestic terrorist acts in 18 Western European countries from 1950 to 1995. This remarkable database is comprised of 10,239 terrorist events which are differentiated on the basis of country, lethality, whether the acts were perpetrated by organized and/or long-lived groups, and the ideology of the group perpetrating them (ethnic, Left wing, or Right wing). Interestingly, Engene's comparison to international terrorist datasets (such as the well-known ITERATE project) shows that the volume of domestic terrorism in Western Europe since 1968 is much greater than the volume of international terrorism during that period, a finding which partially undermines the argument that the "new" terrorism has supplanted the "old." Pearson's r correlations reveal that high levels of democracy, state respect for human rights, and political freedom have general dampening effects on terrorist violence. Uneven income distribution and economic modernization are concluded to be positively associated with terrorist violence, especially ideological terrorism in the latter case. In regards to the factors Engene believes undermine legitimacy, ethnic fragmentation, not surprisingly, increases the likelihood that a state will experience ethnic terrorism, while problems of continuity and integration both significantly increase the prospects of ideological terrorism. In his final substantive chapter, Engene sheds further light on these findings by conducting in-depth case studies of each of the countries under examination, allowing for the specific identification of important trends germane to the hypotheses.

Engene's account of the impetuses for domestic terrorist violence represents a valuable clarification and extension of extant theoretical treatments. Most notably, his "communicative" approach, by delving into the political relations crucial to the success of terrorist movements, reinforces the very important notion that terrorism must be viewed as an activity that results from the same considerations underpinning "normal" political discourse, and not some aberration perpetrated by unthinking zealots. However, the theory suffers from some potentially confounding conceptual problems. In addition to unresolved tautologies in the hypotheses (is terrorism primarily a cause or effect of illegitimacy?) and confusion invited by the inclusion of "pro-state" terror (can/how can one include in this framework actions perpetrated by the state itself to shift bonds of loyalty?), Engene's claim that the state and public are terrorists' only crucial audiences is an oversimplification. As Martha Crenshaw has noted, terrorists actually attempt to communicate with two public audiences when engaging in violence: the members of their "subgroup" – the broader group experiencing the injustice perceived by the terrorists – and the rest of society at large; though he makes passing reference to the subgroup, Engene does not explicitly incorporate it into his theory. From a rational choice perspective of insurgency, if terrorism is observed, the subgroup must be assumed to have made an a priori decision that violence is not the optimal means by which to redress its grievances with the state. Otherwise, "higher" levels of insurgency that involve more numerous participants and rely less on terrorization would likely be observed. Put differently, terrorist violence represents not just the actions of a fringe group, but of a fringe group whose methods are largely unpalatable to a majority of their compatriots.

Ultimately, Engene's failure to systematically distinguish between different portions of the public, because it leads to an overestimation of the amount of support that terrorists' actions enjoy among the people they purport to represent, also leads him to overestimate both the degree to which terrorist violence mobilizes popular support and the difficulties faced by the state in reestablishing legitimacy. For example, a response by the government that is successful at punishing terrorists but concomitantly minimizes alienation of the subgroup can (as did the French government's response of "efficient repression" to initial terrorist attacks by the Algerian FLN in November 1954) reestablish the greater public's faith in the legitimacy of the government by reaffirming both the state's monopoly on force and the rule of law. At the same time, such a response precludes the development of significant bonds between the terrorists and the subgroup (the Algerian population) by bolstering the subgroup's belief that the terrorist's means are illegitimate. If this situation prevails, the terrorist group must drastically change strategy and tactics (as did the FLN, which began to target the subgroup to punish it for collaboration with French authorities) or face imminent failure.

Moreover, some of Engene's analytical methods are deserving of scrutiny. To test his hypotheses, Engene conducts simple correlational analyses between terrorist acts within countries and levels of democracy, ethnic fragmentation, etc., at particular points within the data range (e.g., democracy levels in each country in 1960, freedom levels in 1975), and these analyses are conducted in isolation from one another. This approach is problematic for several reasons. First, Engene does not test for significant correlation between the independent variables; such correlation, which almost certainly exists between such measures as freedom, democracy, and development, could drastically impact the substantive findings taken together. Second, given that these explanatory measures vary not only cross-nationally but longitudinally, and that extensive time series data are available for nearly all the factors under examination (e.g., the POLITY and Freedom House projects, World Bank World Development indicators, and other compilations of economic data), it is perplexing that Engene does not conduct cross-sectional time-series tests of his hypotheses. Although Engene's qualitative analysis bears out many of his contentions, the robustness of his statistical approach would be greatly improved given these modifications.

In all, despite some shortcomings, Engene's study is an important advancement in both the theory and analysis of domestic terrorism. His conceptualization of terrorism as a communicative action undertaken by political actors is lucid and largely convincing. Above all, his TWEED dataset fills a crucial void that has hamstrung empirical scholars of terrorist violence for some time, and represents an indispensable resource for future scholars.

Dennis M. Foster is an Assistant Professor of International Studies and Political Science at the Virginia Military Institute.