Terrorist attacks can lead to increased ethnic segregation – but only for a short while

Jens Rydgren foto Clément Morin
Jens Rygren. Photo: Clément Morin/Stockholm University

Authors: Christofer Edling, Jens Rydgren and Rickard Sandell After suffering terrorist attacks cities like Stockholm, London, Paris, Barcelona, Madrid, Berlin, New York, among others, reacted in the same way: by returning to normality as fast as possible. However, resilience is often an attribute made by journalists covering the aftermath of attacks. Scientific evidence of resilience is less abundant, and tend to focus only on attitudes.

In a paper published in 2016, we provide a scientific account of both attitudes and behavior in reaction to a terrorist attack, showing that also behavior is subject to resilience. We argue that the tragic events in Madrid on March 11 2004 triggered a shift in attitudes toward Arab immigrants, and that this shift had repercussions on the Arab born population’s migration patterns (internal and international) within and to Spain, causing a significant setback in the integration of Arab immigrants in Spain. This analysis describes and documents a clearly detectable shift in migration dynamics after the 2004 bombings, using empirical macro-data at a high level of aggregation. We show that this shift was not permanent but temporary, indicative of something akin to system resilience.

In the morning of March 11, 2004, Madrid’s commuter train system suffered a series of terror bombings. Four commuter trains where hit around 7:40 a.m. with a total of 10 bombs, killing 191 people and leaving close to 2,000 wounded. It was the worst terror attack ever in Spain and one of the bloodiest ever in Europe. It was found that Islamic fundamentalists masterminded the bombings and that several of the offenders were of North African origins. As Spain became a target for Islamist terrorism, Spain’s Arab minority group drifted into the center of attention politically as well as socially.

In our study, we relied on the Estadistica de Variaciones Residenciales assembled by Spain’s National Statistical Agency (INE), and estimate the local immigrant densities quarterly from January 1, 1999 to January 1, 2010. In this time interval 5.4 million international migration events from some 198 different immigrant collectives occurred. Simultaneously 13.9 million intermunicipal migration events took place within Spain. 3.8 million of these events are foreign-borns internal migration. The data also include movements of undocumented immigrants. We consider migration movements between Spains 52 provinces. Hence in the spatial analysis of the evolution of the residential mix, location is equal to province. For those unfamiliar with the Spanish immigration context, the total population from the Arab countries was approximately 460,000 at the time of the attack, and 910,000 at the end of the analyzed period.

Figure 1 below displays the change in integration over the period. Our measure of integration (Theil Information Index) takes into account all changes in the mix of two groups in the defined areas of interest over time. The index varies between 0 (when all provinces have the same composition as the nation at large) and 10 (when all provinces contain one group only). Before the 2004 terror attack, the index shows a clear tendency toward increased integration of the Arab subpopulation (the lower the score, the more evenly distributed is the minority group across Spanish provinces). At the time of the attack, the trend is suddenly reversed. What follows is an increase in segregation. A year after the attack (second and third quarters in 2005), the index score is about 2.5% higher than the score in the second quarter of 2004 immediately after the attack. Three years later, in the first quarter of 2007 and roughly at the time when Spain’s economy comes to a full stop, the index score has returned to its level before the attack. Thus the shift in integration following the attacks was temporary, suggesting system resilience in the face of external shocks.

To exclude alternative explanations of the observed change in residential integration, we also compare the Arab subpopulations’ integration trend with the trend for other immigrants from countries outside the EU. We see that the increased segregation experienced by the Arab subpopulation is unique to this group. This implies that the trend observed for the Arab population is not the result of a general change in residential preferences toward immigrants in Spain. The result supports our hypotheses that integration of the Arab minority group was negatively affected by terror attack. That is, that the Madrid bombings temporarly obstructed the integration of the Arab population in Spain.

Figur 1 Jens
Figure 1. Change in integration (Theil Information Index), 2000 to 2010, and the timing of the Madrid bombings.
Note. EU = European Union.

Figure 2 below provides a detailed analysis of the type of migration—internal or international—that was causing the largest change in the index from one period to another.

Figur 2 Jens
Figure 2. Internal and international migration and change in integration (Theil Information Index).  

From Figure 2 above, we conclude that the trend towards increased segregation is driven largely by immigration to Spain, and to a lesser extent by internal migration within Spain. In other words, in the period immediately after the bombings, new immigrants from the Arab world are more likely than before the bombings to settle into areas were Arabs already live. This type of movement is expected when increased hardship to sustain is present.

Hence, the analyses show that ethnic segregation increased (i.e., the average geographical distance) between Arab immigrants and native Spaniards shortly after the terror bombings. No such effect was found for other immigrant groups. It should be emphasized that this analysis is done on highly aggregate data (on the 52 provinces of Spain) and still a notable change can be recorded. With more fine-grained data on municipalities and neighborhoods, we would expect to pick up even more dramatic changes.

However, and this is perhaps an even more important finding: the empirical analysis shows that this was a relative short-term effect. After about 2 years, ethnic integration started to increase again (and thus resumed the positive trend that was observed during the years before the terrorist bombing). This observation in itself is an indication of how resilient society can be against a terrorist attack.


Edling. C, Rydgren. J. and Sandell R. (2016), “Terrorism, Belief Formation, and Residential Integration: Population Dynamics in the Aftermath of the 2004 Madrid Terror Bombings”, American Behavioral Scientist, 60(10).


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