According to one long-held theory that talks about the South Asia's caste system and how it begun, it is believed that Aryans from central Asia at some point invaded the South of Asia and implemented a caste system as a way to control the invaded populations. The invaders set key roles in society, then assigned the groups of people to those roles. In that way, individuals were born into one of those groups and all their social relations, until the day of their death, would be inside of that group or depending on what it represented. There was no social mobility in that system.