Two notable mass conversions were the sweep of Christianity through the Roman empire in the fourth century and the seventh century military campaign that made Islam the dominant religion from North Africa through the Arab East to India. In most societies in which several religions meet, people pass continuously across the boundary between faiths. Most of these passages can be adequately understood as ideosyncratic events in the lives of persons who were usually marginal to their societies even before their shift of allegiance. With the phenomenon of societal conversion, however, the converts are led by the group's elite. Societal conversion is the assimilation of one group into another.
Cultural assimilation involves accepting the symbols through which group identity is expressed.
Societal conversion follows the decline in the legitimacy of the authority of the group's religious elite. The members of the group then require another source of legitimate authority to sustain social order. The adoption of the new faith by individual members of the group is their adaptation to the new societal circumstance. The study itself clearly documents the cultural assimilation of the American Jewish community and strongly indicates an unmistakable trend towards societal conversion. The overall study projected a figure of 4,210,000 people in the U.S. who were born Jews and whose religion is Judaism.