The greatest challenge to national unity was Mauritania's heterogeneous population. As in all the Sahelian states, Mauritania's southern regions were inhabited mainly by peasants who belonged racially and culturally to black Africa, while the population of its northern regions were desert nomads who identified with the Arab world. At independence, Mauritania's estimated 1.5 to 1.8 million people could be divided into three groups: one-third of the inhabitants were both racially and ethnically Maures; another third, although racially black or mixed Maure-black, were ethnically Maures (this group of black Maures was essentially a slave class until 1980, when slavery was abolished); and the remaining third were racially and ethnically black, resembling in many respects the populations in neighboring Senegal and Mali.[1]