By definition, world religions have always been expanding over the globe and have been a major part of the formation of world civilizations. This expansion has also always been intertwined with histories of trade and conquest as well as with those of learning and education. Since 1800 religious expansion is part and parcel of the spread of modernity. Finally, in today's world it is directly connected to the contemporary process of globalization. The study of conversion and of the globalization of religion gives us an excellent vantage point from which to study these larger transformations. This opportunity has often not been sufficiently realized for reasons that are closely related to these transformations themselves. Secularist assumptions about secular progress and the decline of religion have hindered the development of an adequate understanding of the importance of religion in the modern world.