The Effect of Migration on Terror - Made at Home or Imported from Abroad?

We analyze the causal effect of the stock of foreigners residing in a country on the probability of a terrorist attack in that country. Our instrument for the stock of foreigners relies on the interactions of two sets of variables. Variation across host-origin-dyads results from structural characteristics between the country of origin and the host, while variation over time makes use of changes in push and pull factors between host and origin countries resulting from natural disasters. Using data for 20 OECD host countries and 183 countries of origin over the 1980- 2010 period we show that the probability of a terrorist attack increases with a larger number of foreigners living in a country. However, this scale effect is not larger than the effect domestic populations have on domestic terror. We find scarce evidence that terror is systematically imported from countries with large Muslim populations or countries where terror prevails. Policies that exclude foreigners already living in a country increase rather than reduce the risk that foreign populations turn violent, and so do terrorist attacks against foreigners in their host country. High skilled migrants are associated with a significantly lower risk of terror compared to low skilled ones, while there is no significant difference between male and female migrants.