Complex sentence: Upon returning to Angola in 1966 he formally launched UNITA and began his career as an anti-Portuguese guerrilla fighter, but also fought the FNLA and MPLA, as the three resistance movements tried to position themselves to lead a post-colonial Angola.
Split into simpler sentences: Upon returning to Angola in 1966 he launched UNITA and began his career as an anti-Portuguese guerrilla fighter. He also fought the FNLA and MPLA, as the three resistance movements tried to position themselves to lead a post-colonial Angola.