The Association of Southeast Asian Nations (ASEAN) is a miracle. In an era of growing cultural pessimism, there is a pervasive belief that different civilizations cannot function together. Yet the ten countries of ASEAN are a thriving counter-example of coexistence. Here, more than 625 million people live together in peace.

In 1967, leaders from Indonesia, Malaysia, the Philippines, Singapore, and Thailand struck a landmark agreement, forming ASEAN. They had realized that political and economic cooperation would bring greater stability and prosperity to the region. Fifty years and five...