Was 9/11 the opening salvo in a new age of terrorism? Some argue that this act ushered in a more chaotic world. Others contend an increased focus on terrorism in the past 15 years is the result of conflating terrorist activity with insurgency. We shed light on these claims by analyzing data on domestic and transnational terrorist incidence from 1989 to 2014. The evidence suggests that the years since 9/11 have been different from those preceding them. Once the prevalence of conflicts is accounted for, the post-9/11 era is a significantly less terror prone period than the years before it. A country not suffering civil conflict was upwards of 60 percent more likely to experience terrorism prior to or during the year 2001 than since. However, the opposite trend holds for those countries with a higher proportion of Muslims. Prior to 2001, countries with higher Muslim populations experienced less domestic terrorism. Since 9/11, these countries have experienced significantly more terrorism – both domestic and international – than they had previously.

Introduction In the immediate aftermath of the 9/11 attacks, policymakers were swift in declaring transnational terrorism the next extreme threat to international security.1 Some even gave expression to the notion that 9/11 fundamentally changed the world by framing the conflict between the West and Islamist terror as “World War IV” – a perpetual state of conflict between militant Islam and the West.2 Others have situated the September 2001 attacks within the broader historical context of terrorism. Just as the end of the Cold War heralded a transformation in the phenomenon of terrorism from nationalist, leftist, and often separatist ideologies, 9/11 reflects a shift in the primary motivation for terrorism to the religious and fundamentalist realm.3 Indeed, these narratives tend to comport with a view that the world is more volatile and unstable than it has been in the past—an interpretation often perpetuated by popular media reports. A 2016 article in the New York Times notes that the number of deaths attributed to terrorism in North America and Europe rose markedly in 2015.4 However, the article also adds that more than three-quarters of all terrorism fatalities over the last five years transpired in six countries: Afghanistan, Iraq, Nigeria, Pakistan, Syria, and Yemen – all places beset with civil strife. The latter point is in line with a host of research drawing important connections between terrorism and civil wars (Findley and Young, 2012). Weak or failed states are centers for terrorist activity (Bapat, 2007; Piazza, 2008). Terrorism is a tactic often employed by rebels in civil wars for various purposes (Stanton, 2013). Terrorism may additionally serve as a spoiler to peace processes (Findley and Young, 2015). This research program makes clear that any accounting of terrorism should seek to contextualize it, particularly when the setting of much terror is insurgency and civil war. When one does so, how, if at all, does this impact how we appreciate terrorism since 9/11? In the roughly 15 years since 9/11 and the start of the “global war on terror,” the world experienced more civil and terrorist violence. But is this modern era remarkably different from the one preceding it? Has 9/11 impacted the prevalence of terrorism and its fundamental relationship with civil conflict?5 Furthermore, is such conflict-related terrorism largely domestic or transnational in nature? We leverage data on worldwide terrorist incidence to address these issues. Our results suggest that after accounting for the prevalence of terrorism in conflict settings, the post-9/11 era is much less terror-prone than the years preceding it. We also highlight another shift in terrorist activity from predominantly non-Muslim to Muslim majority countries. Prior to 2002, the higher a country’s Muslim population, the less domestic terrorism it tended to experience. Since 2002, this trend has strongly reversed. And finally, interventions into civil conflicts by Western countries are highly correlated with domestic terrorism.

Research Design For our analysis, we use data on terror events from the GTD.8 The GTD includes approximately 140, 000 terrorism events from 1970 to 2014 and is one of the most extensive sources of data on terrorist attacks.9 The models below specifically examine the years after the Cold War up to 2014. Our unit of analysis is the country-year; and the data include 194 countries.10 Our dependent variable is a count of terrorist incidents in a given country for each year. We further disaggregate this variable to distinguish international or transnational from domestic terrorist attacks, as the two types of terrorist phenomena may have differing causes or impacts (Enders et al., 2011).11 We employ a negative binomial model rather than the traditional Poisson model. This is because our terrorist events data violate the Poisson assumption that the variance is equal to the expected value. Because the variance far exceeds the expected number of occurrences, the data exhibit considerable overdispersion.12 Also, to account for potential dependence within countries over time, we cluster standard errors by country. To reflect the incidence of conflict in a given country, we construct three independent variables from the ACD. The first is a binary indicator reflecting conflict within the borders of a given country in a given year. In the supplementary file we also specify a count variable reflecting the number of conflicts that may be ongoing within a country for each year. Also, to discriminate between conventional war and minor conflicts, we include a conflict variable consisting only of wars exceeding 1000 battle deaths.13 We control for (logged) GDP per capita with data from the World Bank.14 We also control for the (logged) population size. We account for regime characteristics with Polity indicators, ranging from -10 to 10.15 Similar to Robinson et al. (2006), we include a non-time-varying, country covariate for the percent of the Muslim population. Because foreign policy behavior can affect terrorism (Savun and Phillips, 2009) we also control for Western intervention in civil wars. We code a binary measure reflecting military involvement by the USA, the UK, or France on behalf of governments fighting civil conflicts.16 We also create a binary indicator reflecting whether an observation is before or after 9/11. This post-GWOT indictor takes on values of 1 in all years after 2001 and 0 otherwise.17 Finally, as a robustness check we incorporate a count of the number of attacks from the previous year.18

Concluding Discussion Was 9/11 a watershed moment? We have attempted to gain leverage on this question by inspecting terrorist activity in the years before and after the event. Though we strictly examine correlations here, the analysis indicates some meaningful distinctions between the two periods – although in important respects these differences run counter to the oft-cited narrative about 9/11. And while we cannot say that 9/11 precipitated any of the changes we observe, several points merit highlighting. First, terrorism primarily exists within the context of insurgency. The strongest predictor of terrorism within the borders of any given state is the presence of armed conflict, especially for domestic attacks. This result lends credence to the argument that terrorism is primarily a tactic. This result is also in line with Mueller and Stewart’s (2011) argument that, “…terrorism’s apparent incidence, and therefore the seeming importance, has been multiplied by effectively conflating it with insurgency.” Second, it is not just that the balance of terrorism inside and outside areas with active conflict remains tilted toward conflict zones, but that terrorism incidents outside of warzones in the post-9/11 era have decreased in absolute terms. The downward effect is particularly strong for transnational terror incidents. It is entirely consistent with the evidence presented here that this reduction is a consequence of counterterrorism measures enacted since September 2001. However, any number of factors might explain this change. Moreover, this result may ultimately reverse as foreign fighters return to their countries of origin (or migrate elsewhere) from current warzones in places such as Iraq and Syria. Third, we demonstrate a marked shift in terrorism within predominantly Muslim countries. Prior to 2002, states with higher Muslim populaces could expect less domestic terrorism within their borders. Since then, the opposite is true. There is significantly more terrorism – both domestic and international – in predominantly Muslim nations. Jihadist terrorism looks to have become more enduring and widespread in the past 15 years. One explanation for this may be that Jihadi groups have made a strategic decision to focus their fire on the “near enemy” rather than on foreign powers. Another could be that defensive measures in the West have forced a shift in target set. This swing may also owe as much to domestic upheavals in parts of the Muslim world combined with Western responses to them. Islamist conflicts have risen since 2001, and our work here is broadly in line with Gleditsch and Rudolfsen’s (2016) proposition that the increase in conflicts in Muslim countries after 2001, in absolute but especially relative terms, is reflective of a reaction in the Muslim world to interventions by major powers. It is difficult to parse out the singular effects that Western interventions into multi-sided insurgencies in Muslim countries may have on terrorism. Doubtless these interventions suffer selection bias, whereby interveners only participate in the most protracted and pernicious wars. However, consistent with our results is the possibility that the counter-terrorism policies of governments in Muslim majority countries and foreign states intervening militarily on their behalf since 9/11 are provoking more terrorism than they are preventing. Our effort suggests that this may be the case for much of the domestic terrorism plaguing many Muslim countries. This is an obvious area for future work. In sum, this research aims to present a focused and balanced reckoning of the GWOT by comparing it to the era immediately preceding it. The results do not generally comport with popular or mainstream accounts of terrorism. This may be owing to an implicit negative bias in the manner in which terrorist news is reported. Terrorism provokes a pronounced media reaction easily reflected in headlines, often strengthening the public’s sense of threat (Gadarian, 2010). It is not our intention to trivialize the threat of terrorism but to put it in a measured perspective. We hope our effort will spur further analysis and informed debate about an important issue to scholars, the wider public, and those making policy decisions related to terrorism.

Acknowledgements We thank Navin Bapat, Greg Howard, Trevor Johnston, Daniel Kremaric, Jeffrey Martini, Raymond Mercado, John Mueller, Karl Mueller, Michael O’Hanlon, Jan Pierskalla, Arturas Rozenas, Alexander Stephenson, Paula Thornhill, and Alan Vick. We are grateful to Ashley Weiler for research assistance. The views expressed here are our own and do not necessarily reflect those of RAND or the DoD.

Declaration of Conflicting Interest

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article. Supplementary Material

The supplementary files are available at http://journals.sagepub.com/doi/suppl/10.1177/2053168017739757. The replication files are available at http://thedata.harvard.edu/dvn/dv/researchandpolitics.

Carnegie Corporation of New York Grant

This publication was made possible (in part) by a grant from Carnegie Corporation of New York. The statements made and views expressed are solely the responsibility of the author.