Vectors of extremism across the Canada-US border

The idea that Canadian-based terrorists pose a threat to the United States continues to resonate with Americans. We subject this hypothesis to empirical testing by analyzing terrorist-related activity across the Canada-US border. Drawing on 13 cases with 27 terrorist connections, the evidence substantiates the presence of cross-border interactions, but does not confirm common perceptions about America's northern border: there is no consistent threat emanating from Canada. Rather, differentials in the availability of ideas and resources drive threat vectors across the border in both directions. The bulk of violent extremists exploiting these cross-border markets of opportunity do so to propagate terrorism beyond North America.