Do Walls Work? The Effectiveness of Border Barriers in Containing the Cross-Border Spread of Violent Militancy

Since the end of the Cold War, walls, fences, and fortifications have been constructed on interstate borders at a rapid rate. It remains unclear, however, whether these fortifications provide effective security. We explore whether border fortifications provide security against the international spread of violent militancy. Although barriers can reduce the likelihood that militant activity diffuses across international borders, their effectiveness is conditional upon the roughness of the terrain on which they are built and the level of infrastructure development in their proximity. Barriers require intensive manpower to monitor and patrol, and so conditions like rough terrain and poor infrastructure render security activity more difficult. However, rebels and other militants prefer to operate in such difficult areas, ultimately reducing the effectiveness of barriers in containing the international spread of violent militancy. Analyses on newly collated data on interstate border fortifications within a global sample of contiguous-state directed-dyad-years show that border fortifications are only effective in limiting the diffusion of militancy in contexts in which states can plausibly monitor and police their borders. This paper has significant implications for the academic literatures on national security and intrastate conflict, and it also speaks to the broader policy debate over border walls and fences.

Does Violent Secessionism Work?

Recent research suggests that the strategic use of violence may increase a group’s chance of gaining independence. We investigate this topic using comprehensive data on all secessionist movements between 1900 and 2006 and an original data set on the institutional and extrainstitutional methods that secessionists have used from 1946 to 2011. Our analysis yields several important findings. First, strategy depends on context. Not all secessionist movements are the same, and many have legal and/or institutional routes to independence that shape the methods that they employ. Second, no secessionist movement challenging a contiguous state has won its sovereignty without using institutional methods, either exclusively or in combination with extrainstitutional methods. Finally, we identify four successful combinations of secessionist methods and discuss how these movements develop in relation to their strategic setting. Overall, we find no evidence that violence helps a secessionist movement to gain independence.

The algorithmic neuroanatomy of action-outcome learning

Although it is well known that animals can encode the consequences of their actions and can use this information to control action selection and evaluation, it is not known what learning rules control action-outcome (AO) learning. Here we trained participants to encode specific AO associations whilst undergoing functional imaging (fMRI) and used computational modelling to evaluate competing models. This analysis revealed that a Kalman filter, which learned the unique causal effect of each action, best characterized AO learning and found the medial prefrontal cortex differentiated the unique effect of actions from background effects. We subsequently extended these findings to show that mPFC participated in a circuit with parietal cortex and caudate nucleus to segregate distinct contributions to AO learning. The results extend our understanding of goal-directed learning and demonstrate that sensitivity to the causal relationship between actions and outcomes guides goal-directed learning rather than contiguous state-action relations.