  We study the spatiotemporal correlation of terrorist attacks by al-Qaeda,
ISIS, and local insurgents, in six geographical areas identified via $k$-means
clustering applied to the Global Terrorism Database. All surveyed organizations
exhibit near-repeat activity whereby a prior attack increases the likelihood of
a subsequent one by the same group within 20km and on average 4 (al Qaeda) to
10 (ISIS) weeks. Near-response activity, whereby an attack by a given
organization elicits further attacks from a different one, is found to depend
on the adversarial, neutral or collaborative relationship between the two. When
in conflict, local insurgents respond quickly to attacks by global terror
groups while global terror groups delay their responses to local insurgents,
leading to an asymmetric dynamic. When neutral or allied, attacks by one group
enhance the response likelihood of the other, regardless of hierarchy. These
trends arise consistently in all clusters for which data is available.
Government intervention and spill-over effects are also discussed; we find no
evidence of outbidding. Understanding the regional dynamics of terrorism may be
greatly beneficial in policy-making and intervention design.
