About 30,000 fighters from at least 85 countries have joined the Islamic State of Iraq and Syria (ISIS) as of December 2015.Some have argued that economic poverty is linked to ISIS recruitment. Yet,although the great majority of ISIS recruits come from the Middle East and the Arab world, many foreign fighters also come from Western nations, including most members of the European Union, as well as the United States, Canada, Australia, and New Zealand. Authors Benmelech and Klor have found in the data something much more interesting. They argue that countries with a lot of homogeneity will supply more ISIS fighters than countries with more immigrants.
The less ethnically diverse a society is, the more likely outsiders such as immigrants or second- or third generation Muslims are likely to turn to terror.
This is a classic example of Tajfel’s theory of social identity which states that social groups will naturally compare themselves and compete in order to develop a positive self-image. When there’s no heterogeneity, minorities get rejected, cannot form a positive self-esteem, and anger develops, until the tension is released into violence.
The more homogenous the host country is the greater difficulty immigrants such as Muslims from the Middle East experience in assimilating. As other research has shown, isolation induces some of them to become radicalized.
This is why Scandinavian countries, like Finland, supply most of the ISIS fighters. They have a strong social fabric and are hard for immigrants to break into.