The Oromo people (Oromo: Oromoo; Ge'ez: 'oromo; 'Oromo) are an ethnic group inhabiting Ethiopia and parts of Kenya and Somalia. They are the largest ethnic group in Ethiopia and the wider Horn of Africa. According to the 2007 census, they represent approximately 34.5% of Ethiopia's population, while others estimate they make up about 40% of the population. With the total Ethiopian population thought to be over 102 million, the number of Oromo people exceeds 35 million in Ethiopia alone.

In the late 16th and early 17th centuries, conquests by the Abyssinian Empire in southern and southwestern Ethiopia had left a territorial vacuum, allowing the pastoral Oromo to settle in the vacated territories and incorporate socially dislocated peoples into their gada system. As they moved into earlier Islamic hubs, the Oromos increasingly adopted Islam, and in the process markedly grew their Muslim adherent base to become one of the larger such populations in the Horn region. Pastoralist Oromos also took slaves from their own community's urban areas, as well as from other communities. According to the historian Paul E. Lovejoy, slavery was at this time an important aspect of the social, political and economic structure of parts of Ethiopia. The slaves were classified into two groups: "red" slaves who spoke Afroasiatic languages, and "black" ("Negroid") slaves called Shanqalla who spoke Nilo-Saharan languages. The "red" slaves were primarily courtesans and were more expensive; they were given light duties so as to preserve their looks. The "black" slaves were much less expensive, and toiled in the fields and in Christian Abyssinian households. The "red" slaves, among which were Galla individuals, formed the bulk of captives who were exported from Abyssinian territory to the Arabian peninsula and Persian Gulf regions, to Ottoman Empire markets, to Egypt and elsewhere. Young female Oromo slaves served as concubines and household workers, while males were in demand for private armies and servile labor. Oromos too enslaved other ethnic groups. According to a report by Bermudes, in the 16th century, Oromos during their wars were fierce and cruel, mutilating and enslaving the people in the regions they conquered. Emperor Galawdewos battled with Oromos without much success and sought Portuguese help. In the era of Imam Ahmad, according to Bahrey's records, Oromo Luba 'tribes' made war in Dawaro against Adal Mabraq, devastating the region and occupying it. They also took over Fatagar and Faj, forcing its previous inhabitants into slavery. The pagan Galla and animist Sidama or Agew slaves made up the slave caravans coming out of Ethiopia, as slavers avoided Christian or Muslim slaves. The central Amhara provinces were a part of major Afar slave caravan trade routes from the southern and southwestern Galla, Sidama and Gurage regions to the northern and eastern Ethiopia. Thousands of slaves were exported every year by Jabarti, Jalaba, Afar, Somali and Arab merchants as the income from this trade was lucrative. According to Ira M. Lapidus, a professor of Middle Eastern and Islamic History, the Ethiopian slave trade benefited the Muslims, and increased the Islamization of the Oromo people.

what were some of the regions they conquered?
In the era of Imam Ahmad, according to Bahrey's records, Oromo Luba 'tribes' made war in Dawaro against Adal Mabraq, devastating the region and occupying it.