Interestingly, the number of ISIS foreign fighters is positively correlated with a country’s GDP and its Human Development Index.

Why do Foreigners Join ISIS?

About 30,000 fighters from at least 85 countries have joined the Islamic State of Iraq and Syria (ISIS) as of December 2015.

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.

Thousands of fighters from Russia and hundreds from Indonesia and Tajikistan have also joined ISIS.

The recruitment of foreign fighters to join ISIS is a global phenomenon.

Because of the threat ISIS poses to other nations, it is critical to understand the factors that lead foreigners to join this Islamic jihadist state.  Foreign recruits represent a threat to the international community for a number of reasons.

After joining ISIS, they engage in combat in Syria and Iraq. They also can easily return home from combat largely unnoticed on their government-issued passports.

As returnees trained in terrorist tactics and furnished with new connections, these fighters can create terror networks to commit attacks at home.

For example, Abdelhamid Abaaoud, the alleged leader of the cell that committed the Paris attacks in November 2015, visited Syria, returned radicalised, and recruited an extensive network of accomplices to conduct the attacks.

Why have people from all over the world joined ISIS during the last 5 years?

The extreme gravity of this phenomenon leads us to ask:  Why have people from all over the world joined ISIS during the last 5 years?

In a recent research paper with Efraim Benmelech What Explains the Flow of Foreign Fighters to ISIS?, to be published in the journal Terrorism and Political Violence we provided the first systematic analysis of the link between economic, political, and social conditions with the global phenomenon of ISIS foreign fighters.

We combined a detailed data set on the number of ISIS foreign fighters emerging from countries around the world with data on countries’ social, political, and economic indicators.

These indicators capture individual countries’ political freedom, social fragmentation, economic development, inequality, and unemployment.

Figures 1 and 2 provide a preview of the main results of our analysis. Figures 1 and 2 present scatter plots (as well as the estimated linear fit) of the number of ISIS foreign fighters per each country’s Muslim population and measures of economic prosperity such as GDP per capita (Figure 1) and Human Development Index (Figure 2).

The size of the circles in the plots reflects the country’s Muslim population size.

Poor economic conditions do not drive participation in ISIS.

In contrast, the number of ISIS foreign fighters is positively correlated with a country’s GDP per capita and its Human Development Index (a composite statistic of life expectancy, education, and income per capita indicators, which are used to rank countries into four tiers of human development).

A number of relatively wealthy Western European countries have a substantial number of ISIS foreign fighters relative to the size of their Muslim population.

On the contrary, countries with large Muslim populations such as Pakistan, India and Indonesia have very few ISIS fighters relative to the size of their Muslim population.

Interestingly, this relation also holds in absolute terms.

The total number of ISIS foreign fighters from India, Indonesia and Pakistan (with a combined population of over 560 million Muslims) equals 793.

This is lower than the total numbers from Austria, Finland, Denmark, Ireland, Norway and Sweden who jointly have less than 1.4 million Muslim residents and are the countries of origin for over 900 ISIS foreign fighters.

Many foreign fighters come from countries with high economic development

In fact, many foreign fighters originate from countries with high levels of economic development, low income inequality, and highly developed political institutions.

Other factors that explain the number of ISIS foreign fighters are the size of a country’s Muslim population and the degree of its population homogeneity. Interestingly, a substantial number of ISIS foreign fighters come from established Western democracies with very high political rights.


It is also evident that societies with lower levels of ethnic and linguistic fractionalisation contribute more foreign fighters to ISIS relative to the size of their Muslim population.

These conclusions are consistent with those obtained by qualitative analyses of selected samples of ISIS foreign fighters.

Accordingly, second and third generation immigrants from Muslim immigrants can have a hard time integrating into homogeneous, rich and secularised Western societies due to cultural, religious and social differences.

A large number of these immigrants feel alienated and socially excluded in their Western country of residence.

This leads to a process of radicalisation that starts in the West, whereby their feelings of marginalisation and discrimination make them susceptible to fundamentalist interpretations of militant Islam.

In search for belonging and a cause to embrace

Ultimately, they join ISIS as foreign fighters because of this process of radicalisation and in search for belonging and a cause to embrace.

Although it is difficult to theorise exactly why people join ISIS, it is important to pay attention to the role of assimilation when we start thinking about effective interventions.

The evidence in our research warns against the dangers of isolation within homogeneous Western countries, where anger and discontent among Muslim youth who feel marginalised make them prime targets for ISIS recruiters.

Our research findings may offer hope in the battle against terrorism.

Domestic policies and programs that promote assimilation and break down the silos of ethnic ghettos not only open the doors for isolated groups and benefit society as a whole, but they also may serve as the best defense against radicalisation.