David Martin has been one of the leading scholars of secularization theory since the 1960s. In his magnum opus, A General Theory of Secularization (1978), Martin laid out a careful historical sociology of secularization that maintained the limited and highly particularized nature of this cultural process. Even then he doubted that secularization would be inevitable or that secularism would become universal. For him, one of the key factors for understanding how religion fares in the modern world was “social differentiation,” or the increasing autonomy of social spheres. Social differentiation refers to the tendency in modern society for social spheres to be less and less integrated. For example, the separation of church and state is a fundamental manifestation of social differentiation in the modern world. This dynamic has played out differently in different societies, which is why one finds so much variation not only in the West, but also beyond to the rest of the world. To return to the example, the establishment of the Church of England in that country has no comparison in the United States; in Chile, a different balance altogether has been struck.