Brigadier Ansumane Mané's June 1998 mutiny against President João Bernardo 'Nino' Vieira escalated into civil war when Senegalese and Guinean troops intervened on Vieira's side. The November 1998 Abuja Peace Accord, mediated by President Abdulsalami Abubakar of Nigeria, provided for the withdrawal of foreign forces and their replacement by an ECOWAS Interposition Force (ECOMOG-Bissau).
The ECOMOG-Bissau contingent of ~700 troops — Togolese, Beninese, Nigerien and a small Nigerian command element under Brig. Gen. Femi Williams — deployed in February 1999. The mission was undermined by the Mané faction's May 1999 final overthrow of Vieira (who fled to the Portuguese embassy). ECOMOG-Bissau was withdrawn in June 1999. The operation is the least-studied of the ECOMOG deployments but established the precedent of Nigerian-led ECOWAS political mediation in Lusophone West Africa. See Guinea-Bissau relations.