LAUSR

Significance Following the 9/11 attacks, there were large increases in Islamist terrorism driven especially by al-Qaeda, ISIS, and their affiliates. More recently, we have seen an upsurge in right-wing political extremism in countries around the world. Despite the growing research literature generated by these developments, the issue of whether there are systematic differences between political ideologies in the use of violence remains unsettled. We address these gaps by comparing the use of political violence by left-wing, right-wing, and Islamist extremists in the United States and worldwide using two unique datasets. In both datasets we find that individuals and attacks associated with left-wing causes are less likely to be violent. In the worldwide dataset specifically, we find that compared to other ideologies, Islamist extremists engage in deadlier attacks.