Of 34 barriers built worldwide since 1990, 29 were constructed against Muslim-majority targets. Of those 29, 17, or 59 percent, were also initiated by Muslim-majority states. Thus, exactly 50 percent of post-1990 walls separate Muslims from Muslims. <...> Our data suggest that the Muslim world is unique in its “barrier building” tendencies, internally as well as externally. Out of 146 bilateral intra-Muslim boundaries, 17, or roughly 12 percent, feature barriers.