In Old World Encounters, Jerry H. Bentley described "social conversion" as the "process by which pre-modern peoples adopted or adapted foreign cultural traditions." This process could happen in a number of ways, one of which was forced conversion. Voluntary conversion happened when people intentionally decided to adopt certain cultural traditions of other peoples. Sometimes this might happen when an elite decided to maintain their position by adopting certain practices, or it might occur because a cultural practice was particularly beneficial to a people, especially when it allowed for trade benefits to the people that adopted it. But essentially, voluntary conversion was one type of social conversion. All forms of conversion involved syncretism, or cultural compromise.
Source: Jerry H. Bentley, Old World Encounters: Cross-Cultural Contacts and Exchanges in Pre-Modern Times, (New York: Oxford University Press, 1993,) 8.