Ethiopia is mobilising troops from around the country and sending them to the northern Tigray region to fight a powerful ethnic faction that led the ruling coalition for decades. United Nations and regional officials have expressed alarm about the fighting, which they fear could lead to all-out war in Africa’s second most populous nation. Here is a timeline of key events leading up to the conflict: May 1991 - The Ethiopian People’s Revolutionary Democratic Front (EPRDF) topples Colonel Mengistu Haile Mariam, head of a Communist junta that ruled the country from 1974. The coalition is led by the Tigray People’s Liberation Front (TPLF), guerrilla fighters who marched from their homeland in Ethiopia’s north to the capital Addis Ababa. August 1995 - The Federal Democratic Republic of Ethiopia is proclaimed. The EPRDF sweeps to power in poorly contested elections, and TPLF leader Meles Zenawi becomes Ethiopia’s first prime minister. Tigrayans dominate senior ranks of government. 1995 to 2012 - Meles introduces a system of ethnic federalism, giving the country’s main ethnic groups the chance to govern the areas in which they dominate. Though Tigrayans make up about 5% of the population, they benefit disproportionately, other regions complain, as roads and other infrastructure are built in their sparsely populated area. August 2012 - Meles dies in office. A prime minister from another ethnic group is appointed. 2015 to 2018 - Divisions break out in the EPRDF over how quickly to pursue political reforms in response to street protests that threaten the coalition’s grip. April 2018 - Abiy Ahmed, an Oromo, takes over as prime minister, winning praise at home and abroad for opening up one of Africa’s most restrictive political and economic systems. 2019 - Tigrayans complain they are persecuted in a crackdown on corruption and past abuses. Former senior military and political officials are put on trial. Oct. 11, 2019 - Abiy is awarded the Nobel Peace Prize for his peacemaking efforts, which ended two decades of hostility with Eritrea. The TPLF continue to view Eritrea as an enemy. Nov. 21, 2019 - Ethiopia’s ruling coalition agrees to form a single party, but the TPLF refuses to merge with three other ethnic-based parties, calling the move rushed and undemocratic. Sept. 8, 2020 - Tigray holds regional elections in defiance of the federal government, which postponed nationwide polls due in August because of COVID-19. Abiy’s government says the vote is illegal. October 2020 - The federal government starts to withhold some funds meant for social welfare programs in Tigray, part of a plan to starve the regional authorities of cash in retaliation for September’s vote. Nov. 4, 2020 - Abiy sends troops into Tigray, accusing the TPLF of attacking federal troops based in the region. The TPLF accuses Abiy of punishing the region for the September vote.