While the expanding network of Jesuit missions "provided a measure of protection from the slavers who made annual expeditions into the interior," they simultaneously altered "the mental and material bases of Amerindian culture forever." While tapuios were "nominally free" (or free in name) at the missions, they were actually "obliged to provide labor to royal authorities and to colonists, a practice that frequently deteriorated into forced work hardly distinguishable from outright slavery." The aldeias also proliferated the "spread of European diseases, such as whooping cough, influenza, and smallpox, against which native populations had no immunity," which "killed tens of thousands of Amerindians" and pressured others to retreat deeper into the interior.
