The umbrella body for relations among all African countries is

The umbrella body for relations among all African countries is the African Union (AU). Established in 2002 as the successor to the Organisation of African Unity (OAU, founded in 1963), the AU is a continental organisation whose membership includes all 55 internationally recognised African states.

The AU's objectives include promoting unity and solidarity among African countries, defending their sovereignty and territorial integrity, accelerating political and socio-economic integration, and encouraging international cooperation. Its headquarters is in Addis Ababa, Ethiopia.

The other options do not serve as the umbrella body for all African countries:

• The Commonwealth is an association of former British colonies and territories from across the world, not limited to or inclusive of all African countries.
• ECOWAS is a regional body limited to West African states only.
• The UNO (United Nations Organisation) is a global body that includes countries from every continent, not specifically an African umbrella organisation.

The AU is the only organisation whose membership is specifically designed to encompass every African nation.