Factbox: Ethiopia's main ethnic groups Reuters Staff ADDIS ABABA (Reuters) - Ethiopia’s Prime Minister quit on Thursday, saying he wanted to smooth the route to further political reforms. The government is dominated by the EPRDF coalition led by ethnic Tigrayans. Hailemariam Desalegn’s unexpected resignation followed unrest in the Horn of Africa country initially sparked by opposition in the central Oromiya region to an urban development plan that ethnic Oromos said would encroach on their land. The anger broadened into wider public protests, while bouts of ethnic clashes have also taken place, displacing hundreds of thousands since September. Following are key facts about the main ethnic groups in Ethiopia, Africa’s second most populous nation and a racially diverse country that took its present form from territorial expansions of the 19th century: * Oromos - Oromos make up 34 percent of Ethiopia’s 100 million people but have not held power in its modern history. Analysts say the violence has triggered a resurgence of ethnic Oromo nationalism. Following recent unrest, much of it in the Oromia region, Ethiopia’s new premier is expected to hail from the province. * Amharas - Amharas were the traditional rulers under the era of Ethiopian monarchy that ended with the Soviet-backed overthrow of Emperor Haile Selassie in 1974. Ethiopia’s second largest ethnic group with at least 20 million people, the Amhara claim they are increasingly politically marginalized. The highest-ranking Amhara in the ruling coalition is Deputy Prime Minister Demeke Mekonnen. Amharas hail from the northern and central highlands. * Tigrayans - Tigrayans account for just 6 percent of the population but have dominated politics and the security forces since Tigrayan rebels under Meles Zenawi toppled Marxist military leader Mengistu Haile Mariam in 1991. Tigrayan officials dismiss claims of unbridled control over the ruling coalition, the Ethiopian People’s Revolutionary Democratic Front (EPRDF), but acknowledge the necessity to widen the political space. Tigray is the northernmost of Ethiopia’s nine regions. * SNNPR - The Southern Nations, Nationalities and People’s Region, located in the southwest abutting Kenya and South Sudan, is home to more than 40 ethnic groups, including Hailemariam’s Wollayta. Defense Minister Siraj Fegesa is also from the SNNP. * Somalis - The dry and arid Somali region, also known as the Ogaden, occupies the eastern third of the country and is home to 6 million people. It has a history of separatist rebellion against Addis Ababa, fueled in large part by resentment at its low level of development. However, its recent leadership has been seen as closely linked to Hailemariam and Meles Zenawi before him. Reporting by Aaron Maasho; Editing by Ed Cropley and John Stonestreet Our Standards:The Thomson Reuters Trust Principles.