[2][3] Because of Teixeira and other Portuguese who pushed into the depths of the Amazon, Portugal was able to obtain far more of South America from their Spanish competitors than the Treaty of Tordesillas had granted in 1494.

[2][3][6] In 1617, he also led attacks against the Tupinambás, aiding an ongoing campaign by Portuguese settlers in Maranhão, with the goal of a clearing a land road between Belém and São Luis.

During this period, Bento Maciel Parente made an attempt to take the captaincy for himself by force, but facing resistance by Pedro Teixeira, left for Maranhão.

Parente was later granted the position by the Governor of Brazil, and immediately gave orders for Teixeira to leave and lead another expedition against the natives.

[2][3][8] In 1626, Manuel de Sousa d'Eça, Capitão-Mor of Pará, ordered Pedro Teixeira to procure native slaves.

[2][3][9] In 1637, two Franciscan friars, André de Toledo and Domingos de La Brieba, under threats from nearby natives, abandoned their mission on the Amazon River and, with six soldiers, paddled a canoe up the entire length of the river to the Portuguese settlement of Gurupá, from where they left to Belém, and later to São Luís.

[10] Consequently, the governor of Maranhão, Jácome Raimundo de Noronha, commissioned an expedition with the goal of discovering the river all the way to Quito, learning the best places to establish fortifications, securing through the good conduct of the expeditionaries and small gifts the peace and friendship of the indigenous tribes, and founding a settlement to mark the limit, in the Amazon, of Portuguese control.