Border Walls, Refugees and Terrorism
Are physical walls between countries effective at reducing terrorist attacks? Despite their prohibitive cost and political divisiveness, walls between contiguous countries
have proliferated as extreme forms of border control over the last decades. While the visibility of walls in the public debate has increased, their effectiveness at mitigating
the alleged refugee-terrorism nexus is largely unknown. We use the most updated dataset on walls between adjacent countries worldwide (1975-2016), and
rely on the staggered construction of walls across some country-dyads over time as an identication strategy. The results reveal a strong backfiring effect of walls
over time: attacks substantially increase after the erection of a wall, especially when the refugee stock from contiguous countries hosting transnational terrorist
organizations is larger. We explore potential mechanisms to account for this finding, and point out to the deterioration of in-group vs out-group dynamics as the main reason
behind the backfiring effect of walls.