Of course you wouldn't expect an equal number of mixed race marriages as intraracial ones. You would, however, expect a high percentage of the minority group to eventually be married to partners outside of their group. We see this with Jews in the West, who marry non-Jews at high rates now that religious rigor is relaxing and anti-Jewish sentiment is less normal.

Insularity is common among immigrants, but it normally does not last more than a few generations due to assimilation. The exceptions seem to happen when the group is legally made into a racial underclass or when insularity is a tenet of the group's religion.