The precolonial history of Guinea Bissau is blended with the one of the Sudanese empire of Mali, which was responsible for the establishment of the country's coastal regions.
In the XIIIth century the Sudanese Emperor Surianita Keita sent his general Traore to conquer the Wolof of Casamance (Southern Senegal). Its invasion pushed the Djolas, Banhuns, Paper, Cassangas, Manjacos and Balantas to the coast, becoming the early inhabitants of Guinea Bissau.
The expansion of the empire continued and quickly incorporated the savannas of northern and western Guinea Bissau: Braco would later be called Farid by the Portuguese and Gabú. Political control of these two administrative subdivisions gave commercial control of the area to Mali and the regions around the Geba and Corubal became major producers of salt and gold for the trans-Saharan trade and also unwrapped trade between different ethnic groups. The Balanzes became farmers and producers of salt and the Manyacos specialized in the production of the oil of African palm.
The Portuguese interests in Guinea Bissau began in the XVth century with the trip of Nuno Tristao to Senegal and to the Big river of Bubo in 1444. In another Portuguese expedition the Italian Aluisi Casamosto discovered the current Guinea Bissau, entering the rivers of Cacheu and Mansoa and crossing the Bissagos Archipel. In 1546, the Cape Verde Islands were discovered by Diego Gómez and Antonio de Nóli, who established there a colony for commercial purposes.
At this point Guinea was the second country, after Ghana, in gold supply. Short after, the Portuguese in Cape Verde moved to Guinea Bissau to be closer to the source of commerce and managed to avoid the control of Lisbon for over a century.
They were helped by young Africans who adopted the Portuguese customs and converted to the Catholicism, creating the Creole language, spoken by most of the population in Guinea Bissau.
When gold reserves were depleted in the XVIth century, slavery became the main source of trade on the coast of Guinea. In 1616, Portugal established a military post in Cacheu as slave's center. Until the XVIIth century more than five thousand slaves had been embarked in this region towards Cabo Verde. During this period the Mandingas dominated the slave trade by attacking the Djolas especially to enslave and sell them.
The Papels and the Biyagos were very aggressive: they captured the Felupes, the Baiotes, the Manyacos and Biafadas which were sold directly to African traders.
The second period of the slave trade, from the XVIIIth century on, was dominated by France and England in the Senegambia, by the Fulbe in the Western regions of Guinea and by Portuguese efforts to maintain its hegemony reinforcing the control over Bissau.
Portuguese traders eventually lost because French merchants offered better prices and higher quality goods. Meanwhile, the Fulbes stopped being nomadic and became a political power capable to dominate the Mandingas in the Northeast and the Beafadas in the Southeast.
In 1880, due to a massive economic depression, Portugal was forced to cede the Casamance region to France, trying to keep the rest. It adopted repressive measures to put the Cape Verdeans in positions of authority. It tried to lure Portuguese immigrants, but failed because they preferred the better climates in Angola and Mozambique, causing low investment in Guinea Bissau.
In 1926 with the advent of the government of Salazar the economic control was reinforced in this colony and from 1940 the country entered a crisis from which never recovered and that culminated with the independence war in 1974.