For decades, social psychologists have explored the processes that lead social groups to achieve oneness and uniformity. For instance, some researchers have investigated the way in which social groups transmit and maintain shared norms and standards (Crandall, 1988; Sherif, 1936). Others have studied the pressures to conform to majority views (Abrams et al., 1990; Asch, 1956) or to obey leaders and authorities (Milgram, 1974). With regard to the field of group decision-making, a substantial body of work has addressed the processes leading group members either to polarize their opinions (Brauer & Judd, 1996; Moscovici & Zavalloni, 1969) or to overlook alternative courses of action because of striving for unanimity (Janis, 1972). Finally, social psychologists have also explored the way in which groups achieve cohesiveness (Hogg, 1992; Lott & Lott, 1965) and people's tendency to loose their sense of individual identity when acting in group situations (Diener, 1979; Zimbardo, 1970).
Undoubtedly, these processes are of central importance for group life and deserve to be studied in depth. However, despite a clear tendency to cohere and to seek consensus, most social groups are internally divided into subgroups (Hornsey & Hogg, 2000). What is more, in some situations the members of a subgroup may decide to undergo a schism; that is, they may leave the parent group either to form a breakaway group or to join a different group.