Chad is a landlocked country in north-central Africa, officially known as the Republic of Chad. Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon to the southwest, Nigeria to the southwest, and Niger to the west form the country's borders. Chad is divided into three regions: the desert in the north, the arid Sahelian belt in the center, and the more fertile Sudanian Savanna zone in the south. The country's name comes from Lake Chad, Africa's second-largest wetland. N'Djamena, the capital, is the largest city. Arabic and French are the official languages of Chad. There are over 200 cultural and linguistic groups that call it home. The major religions practiced in Chad are Islam and Christianity. Human populations began to migrate into the Chadian basin in large numbers beginning in the 7th millennium BC. By the end of the first millennium AD, Chad's Sahelian strip had seen a succession of states and empires rise and fall, each vying for control of the trans-Saharan trade routes that passed through the region. By 1920, France had invaded the region and integrated it into French Equatorial Africa. Under the leadership of François Tombalbaye, Chad gained independence in 1960. In 1965, resentment of his policies in the Muslim north resulted in the outbreak of a long-running civil war. The rebels took control of the capital in 1979, ending the South's hegemony. The rebel commanders, on the other hand, fought among themselves until Hissène Habré defeated his opponents. The Libyan invasion started the Chadian–Libyan conflict in 1978, and it ended in 1987 with a French military intervention. In 1990, Hissène Habré was deposed by Idriss Déby, his general. In 1991, the Chad National Army was modernized with the support of the French. Since 2003, the Sudanese Darfur crisis has spilled over the border, destabilizing the country. Already impoverished, the country and its people have struggled to absorb the hundreds of thousands of Sudanese refugees who have set up camp in and around eastern Chad. While several political parties are involved, power remains firmly in the hands of the governing Patriotic Salvation Movement, which was previously headed by President Déby, whose authoritarian rule lasted decades. Political unrest and attempted coups d'états continue to haunt Chad. It is a developing nation, with one of the lowest Human Development Index scores. Chad is one of the world's poorest and most corrupt nations, with the majority of its people living in poverty as herders and farmers. Since 2003, crude oil has surpassed the conventional cotton industry as the country's primary source of export earnings. Chad's human rights record is dismal, with illegal detention, extrajudicial killings, and restrictions on civil liberties perpetrated by both security forces and armed militias. FACT rebels assassinated President Déby in April 2021.