The Ethiopian highlands hold a Christianity that has been continuously established since the fourth century, with its own canon that includes books preserved nowhere else, its own liturgical language in Ge'ez, its own musical notation and chant tradition, a monastic system of great antiquity, and practices including a strict fasting calendar and the veneration of the tabot in every church.
Around and against it, the nineteenth and twentieth centuries reshaped religious life across the whole region. Protestant and Catholic missions arrived with and sometimes ahead of colonial administrations, established schools and clinics, reduced dozens of languages to writing, and produced Christian populations that in several countries are now majorities. The East African Revival, beginning in Rwanda and Uganda in the 1930s, spread a lay movement of public confession and personal transformation across the Great Lakes and left a permanent mark on the region's Protestantism.
Independent and prophetic churches grew alongside. Islam expanded inland from the coast along trade routes and is now the majority religion in Somalia, Djibouti and Comoros and a very large minority in Ethiopia, Tanzania and Kenya.
The indigenous traditions did not vanish, and in several cases have been reasserted politically. Irreecha now draws crowds in the millions and has become a focus of Oromo identity, and the gada system was inscribed by UNESCO in 2016 as an indigenous democratic institution.