Online radicalization through extremist content has surged globally, with thousands joining ISIS after viewing such material online.

\nThis study explores if anti-Muslim hostility explains support for ISIS in Western Europe. Using geo-referenced data on the digital activities of sympathizers across France, UK, Germany, and Belgium, we analyze local-level anti-Muslim animosity's link to pro-ISIS actions on Twitter.

Findings:

\u2014 Local hostility strongly correlates with online radicalization indicators. Pro-ISIS tweets increase when there are terrorist attacks, propaganda releases, or anti-Muslim protests nearby.

Methodology: \nThe analysis relies on high-frequency data tracking user engagement and event timing to establish this connection.

This evidence suggests that addressing local prejudices is crucial for countering ISIS recruitment in Europe.