One of the most important and complicating factors in defining ethnicity is the dramatic increase in the internal migration of Sudanese within the past twenty years. It has been estimated that in 1973 alone well over 10 percent of the population moved away from their ethnic groups to mingle with other Sudanese in the big agricultural projects or to work in other provinces. Most of the migrants sought employment in the large urban areas, particularly in the Three Towns, which attracted 30 percent of all internal migrants. The migrants were usually young 60 percent were between the ages of fifteen and forty-four. Of that number, 46 percent were females. The number of migrants escalated greatly in the latter 1980s because of drought and famine, the civil war in the south, and Chadian raiders in the west. Thus, as in the past, the migrants left their ethnic groups for economic, social, and psychological reasons, but now with the added factor of personal survival.

Another ethnic group involved in migration was that of the Falashas, who were Ethiopian Jews. In January 1985 it was revealed that the Sudanese government had cooperated with Ethiopia, Israel, and the United States in transporting several thousand Falashas through Sudan to Israel. Their departure occurred initially on a small scale in 1979 and 1982 and in larger numbers between 1983 and 1985. In Sudan, the Falashas had been placed in temporary refugee settlements and reception centers organized by the Sudanese government.

In addition to the problems of employment, housing, and services that internal migration created, it had an enormous impact on ethnicity. Although migrants tended to cluster with their kinsfolk in their new environments, the daily interaction with Sudanese from many other ethnic groups rapidly eroded traditional values learned in the villages. In the best of circumstances, this erosion might lead to a new sense of national identity as Sudanese, but the new communities often lacked effective absorptive mechanisms and were weak economically. Ethnic divisions were thus reinforced and at the same time social anomie was perpetuated.

Refugees from other countries, like internal migrants, were a factor that further complicated ethnic patterns. In 1991 Sudan was host to about 763,000 refugees from neighboring countries, such as Ethiopia (including about 175,000 soldiers, most of whom fled following the overthrow of the Ethiopian government in May 1991) and Chad. Approximately 426,000 Sudanese had fled their country, becoming refugees in Kenya and Ethiopia. Many of them began returning to Sudan in June 1991. Incoming refugees were at first hospitably received but they gradually came to be regarded as unwelcome visitors. The refugees required many social services, a need only partially met by international humanitarian agencies, which also had to care for Sudanese famine victims. The presence of foreign refugees, with little prospect of returning to their own countries, thus created not only social but also political instability.

Data as of June 1991