Ethiopia, officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is bordered by Eritrea to the north, Djibouti and Somalia to the east, Sudan and South Sudan to the west, and Kenya to the south. With over 91,000,000 inhabitants, Ethiopia is the most populous landlocked country in the world and the second-most populated nation on the African continent. It occupies a total area of 1,100,000 square kilometers, and its capital and largest city is Addis Ababa. Ethiopia is one of the oldest locations of human life known to scientists and is widely considered the region from which Homo sapiens first set out for the Middle East and points beyond. Tracing its roots to the 2nd millennium BC, Ethiopia was a monarchy for most of its history. Alongside Rome, Persia, China and India, the Kingdom of Aksumwas one of the great world powers of the 3rd century. In the 4th century, it was the first major empire in the world to officially adopt Christianity as a state religion. During the late 19th-century Scramble for Africa, Ethiopia was the only African country beside Liberia that retained its sovereignty as a recognized independent country. It was one of only four African members of the 20th-century League of Nations established following World War I. When other African nations gained their independence following World War II, many of them adopted the colors of Ethiopia's flag. Addis Ababa became the base for several global non-profit organizations focused on Africa. In 1974, at the end of Haile Selassie I's reign, Ethiopia became a federal republic ruled by a military junta known as the Derg, based on communism. In 1987 Mengistu established the Ethiopian People's Democratic Republic which survived until being defeated by a coalition, loosely called the EPRDF. It had ruled since 1991. Ethiopia is a multilingual and multi-ethnic society of around 80 ethnic groups, with the two largest being the Oromo and the Amhara, both of which speak Afro-Asiatic languages. Ethiopia's ancient Ge'ez script, also known as Ethiopic, is one of the oldest alphabets still in use on the continent. The Ethiopian calendar, which is seven years and about three months behind the Gregorian calendar, co-exists alongside the Oromo calendar. The majority of the population is Christian and a third is Muslim; the country is the site of the first Hijra in Islamic history and the oldest Muslim settlement in Africa at Negash. A substantial population of Ethiopian Jews, known as Beta Israel, resided in Ethiopia until the 1980s but most of them have since gradually emigrated to Israel. Ethiopia is also the spiritual homeland of the Rastafari movement. Nine UNESCO World Heritage Sites have been designated in the country. Ethiopia is one of the founding members of the UN, the Non-Aligned Movement, G-77 and the Organisation of African Unity, with Addis Ababa serving as the headquarters of the African Union, the Pan African Chamber of Commerce and Industry, UNECA and the African Standby Force. Despite being located at the headwaters of the Nile, Ethiopia underwent a series of famines in the 1980s, exacerbated by civil wars and adverse geopolitics. The country has begun to recover, and it now has the largest economy by GDP in East Africa and Central Africa.