 The Portuguese attempted to get a larger share of the gold production and trading by establishing a larger presence in the Zambesi valley and by taking aggressive military action against small Muslim controlled sultanates along the coasts of East Africa.By late 16th century, particularly after Francisco Barreto 1569-1575 expedition, the Portuguese had gained control of all the major mining and trading regions along the Zambesi valley where Sena people have lived.In the 17th and 18th-century, conflicts grew as did new causes for it.