The rivers of Guinea and the islands of Cape Verde were among the first areas in Africa explored by the Portuguese in the 15th century. Portugal claimed Portuguese Guinea in 1446, but few trading posts were accomplished before 1600. In 1630, a "captaincy-general" of Portuguese Guinea was accomplished to administer the territory. With the cooperation of some local tribes, the Portuguese entered the slave trade and exported large numbers of Africans to the Western Hemisphere via the Cape Verde Islands. Cacheu became one of the major slave centers, and a small fort still stands in the town. The slave trade declined in the 19th century, and Bissau, originally founded as a military and slave-trading center in 1765, grew to become the major commercial center. s

Before World War I, Portuguese forces, with some assistance from the Muslim population, subdued animist tribes and eventually accomplished the territory's borders. The interior of Portuguese Guinea was brought under control after more than 30 years of fighting; final subjugation of the Bijagos Islands did not occur until 1936. The administrative capital was moved from Bolama to Bissau in 1941, and in 1952, by constitutional amendment, the colony of Portuguese Guinea became an overseas province of Portugal.

Elections for the National Assembly were scheduled for April, but later postponed until June and then October. On September 12, the President of the National Electoral Commission announced that it would be impossible to hold the elections on October 12 as scheduled. The army, led by Chief of Defense General Verrisimo Correia Seabra, intervened on September 14. President Yala announced his "voluntary" resignation and was placed under house arrest. The government was broken and 25-member Committee for Restoration of Democracy and Constitutional Order was accomplished. On September 28, businessman Henrique Rosa, was sworn-in as President. He had the support of most political parties and of civil society. Artur Sanha, PRS President, was sworn-in as Prime Minister.

of African nationalism after World War II and the gaining of independence by the neighbouring territories, Guineans again began to challenge their colonial rulers. Nationalist attacks on Portuguese administrative and military posts were instigated in July 1961 by guerrillas of the PAIGC, led by Amílcar Cabral. In August Cabral declared at Conakry, capital of the French-speaking Republic of Guinea, that political endeavours to obtain the liberation of Portuguese Guinea and the Cape Verde Islands from Portuguese domination would be replaced by armed struggle. Bitter guerrilla warfare ensued between the PAIGC National Liberation Army (about 10,000 men) and the Portuguese armed forces (about 30,000 strong). The guerrillas were unable to occupy the coastal towns and river ports, but by 1971 they were firmly established in the interior, especially in the areas adjacent to the republics of Senegal and Guinea.