People segregate for reasons of security, unity and unification against the majority or other competitive racial groups. Other purposes could be--business, religion, customs, food, style of living, language, worship places, habits, culture, etc.
Long ago ,I remember going to a place in NYC where I went to buy cheaper suit cases etc was replete with Jewish community. At another place, Jackson Heights, I found almost all Sikhs running shops and selling at very cheap prices. Similarly there are China Towns and other settlements.....Even in Missisuaga Canada one can find huge concentrations of Indo-Pakistani's..
Normally these ''segregated groups'' would economically mix up with the majority people, particularly due to food, culture, language, custom and religious reasons.