Of the estimated 38 million Sudanese, more than 5 million live in Greater Khartoum. About 40% of the population are younger than 15 years old. Despite Arabic being the main language and Islam the main religion, the Sudanese society is multiethnic, and ethnicity is a major factor in collective and individual identities. Reportedly, the country has about 600 ethnic groups that speak over 400 different languages and dialects.
The present-day Arabic majority is often described as descending from migrants who came from the Arabian Peninsula and who have intermarried with indigenous populations since the Middle Ages. This, however, is just one perspective and indigenous populations probably form the main substratum of today's society, but they have been thoroughly reshaped by various episodes of migration and profound processes of Arabisation. The mobility inherent in this history shows in the genealogical ties which many ethnic groups claim to have with tribes in neighbouring countries and regions such as Chad, Libya, Egypt and the Arabian Peninsula.
An ethnic group which gained particular international attention was the Nubians, who continue to live in the Nile valley in southern Egypt and northern Sudan. They were greatly affected by the construction of the Aswan High Dam in the 1960s, as its reservoir flooded major parts of their homeland. Many Nubians on the Sudanese side were re-settled to New Halfa in southeastern Sudan. Today, Nubian communities still live in what is often called the Nubian Nile valley which reaches up to ad-Dabbah, north of the Great Nile Bend.
In terms of global dynamics, most of Sudan's migration flows originate from or are destined to neighbouring African countries and the Arabian Peninsula. Saudi Arabia and other gulf states host approximately a million Sudanese labour migrants. While migration of Sudanese to the EU is very limited, up to half a million Sudanese live in bordering states such as Egypt, Chad and Ethiopia. Despite being a refugee-generating country, Sudan also hosts a substantial refugee population. The majority of these come from Eritrea, Ethiopia, Chad and, most recently, Syria.