Religious traditions and communities have always been global. From ancient times, religious beliefs and customs would travel wherever people migrated, from one region to another, settling in disparate locations around the globe. Religious ideas and practices would also travel on their own, passed on from place to place and transmitted far from their communities of origin. The great historian of religion, Wilfred Cantwell Smith, described one such global transmission, the common religious practice of using prayer beads, an idea that spread from meditating Brahmans to chanting Buddhist monks and then to pious Muslims and observant Catholics, who took those transient beads and made them into the rosary, its users unaware of its multireligious global heritage.

Virtually, no part of the world is unaffected by the ideas ...