Cape Verde and Guinea-Bissau campaigned together for independence from Portugal, chiefly led by Amílcar Cabral's Marxist African Party for the Independence of Guinea and Cape Verde from 1956. Cape Verde provided the bourgeoisie that led the anti-colonial movement in Portuguese Guinea. An ideology of unity was key to Cabral's theory of African liberation, and Cabral was himself Cape Verdean Guinea-Bissauan, though the call for unity was partly a tactic to avoid Guinea-Bissau becoming independent without Cape Verde, as the latter had closer ties to Portugal. The PAIGC then fought the Guinea-Bissau War of Independence (part of the wider Portuguese Colonial War), and declared independence in 1973, being formally granted independence in September 1974. Cape Verde joined Guinea-Bissau in independence from Portugal when it peacefully negotiated independence on 5 July 1975, following the April 1974 Carnation Revolution in Portugal, and Aristides Pereira of the PAIGC became president. The intent was unification, as written into the two countries' constitutions. The PAIGC viewed them as "sister republics" with "two bodies with only one heart", and the countries shared a flag and national anthem.