Prior to European Contact, the Amazon Basin was showing signs of early civilization. A number of large settlements along the river traded with one another, and had similar art styles. Large towns existed, and practiced argiculture in the form of farming. So, what if they devoloped into something along the lines of the South-East Asians? Or just on the other side of the Andes? They also have a large East-West trade area, which according to Jared Diamond is what's needed for cultural devolopment.