João Bernardo "Nino" Vieira was elected in 2005 as President of Guinea-Bissau as an independent, being declared winner of the second round by the CNE (Comité Nacional de Eleições). Vieira returned to power in 2005 six years after being ousted from office during a civil war. Previously, he held power for 19 years after taking power in 1980 in a bloodless coup. In that action, he toppled the government of Luís Cabral.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What year did Vieira first assume power?
1980