Explanation: With the arrival of the Europeans came diseases (including smallpox) to which the native peoples had no historical immunity. The Aztecs would have engaged in some warfare, but not enough to lead to such a steep decline (A). Though there was some slash-and-burn agriculture, they primarily used chinampas and terraces (B). Slavery had traditionally been part of Mexican culture, as seen in the Aztec Empire (D). The Europeans used native Mexicans as forced labor, but not until later.