One of the ways in which Christian groups responded to the challenges of modernity was by positioning themselves differently in space. In the interest of better understanding that process, let us think for a moment about the social system, the social space to be precise, within which groups exist. As one starting point for that, it is useful to acknowledge that social groups define themselves in relation to others. Specifically, groups define themselves by saying what they are not as much as by saying what they are. If we are to believe the German social systems theorist Niklas Luhmann, a leading advocate of the notion of social system, difference is prior to identity. That is to say—and this is the core of Luhmann's “difference” theory—one distinguishes a table from other objects before one indicates what it is (Luhmann adds, paradoxically, that distinction presupposes itself). His grand theory has shortcomings, but his point is that social groups create and maintain collective identity by defining themselves in relation to other groups, and especially by saying what they are not. They push off from other groups in defining themselves. We could extend that approach by stating that groups sometimes behave as if they lack a clear collective self-understanding; that is, they lack a fully formed core identity that they can marshall in a positive fashion against a field of other groups. They accordingly define themselves in relation to other groups, define themselves via negativa, by differentiating—in some cases to a great degree—from other groups. Identity is built through such negative definition. The twentieth-century American theorist of social conflict Lewis Coser described that mode of thinking in The Functions of Social Conflict, an extended mediation on the social conflict theories of Georg Simmel, and sociologist of religion Martin Reisebrodt has observed more recently how Christianity invents itself principally by distinguishing itself from other religious practices and beliefs. The process is evident among Christian groups in modernity as it was in early modern Europe. When we focus on how it has manifested spatially, we see the modern in American church history as a broad spectrum of occurrences demonstrating complexity, multivalence, competition, and differentiation.