Auto-segregation or self-segregation is the separation of a religious or ethnic group from the rest of society in a state by the group itself. This could also mean inability for a normal social interaction and a form of social exclusion.
Through auto-segregation, the members of the separate group can establish their own services, and maintain their own traditions and customs. For example, some of the world's uncontacted peoples have preferred not to interact with the rest of the globally integrated human population. By remaining in a reserve and in isolation, they can preserve their cultures intact as long as they choose and the surrounding states protect them.
On the other hand, some groups self-segregate to avoid integrating with other groups, either to protect their culture or some may self-segregate from others that they consider intellectually and/or socially inferior. Nationalists (non-racists) or racists, ultranationalists, different Hindu castes and other 'supremacist' or ethno-centric groups commonly segregate themselves from other communities through various practices like endogamy. The apartheid system in South Africa was an example of this trend.
Endogamy, the practice of marrying within a group, encourages group affiliation and bonding. It is a common practice among displanted cultures attempting to make roots in new countries whilst still resisting complete integration, as it encourages group solidarity and ensures greater control over group resources (which may be important to preserve when a group is attempting to establish itself within an alien culture).
However endogamy can also serve as a form of self-segregation and helps a community to resist integrating with surrounding populations. It thus helps minorities to survive as separate communities over a long time, in societies with other practices and beliefs.
Ethno-religious groups which have successfully resisted complete integration for the longest, for example the Romani (colloquially referred to by non-members as "Gypsies"), the Ashkenazi Jews of Europe and the white people of South Africa, practice a higher level of endogamy.