Early twentieth-century archaeologists accepted the concept of “Nuclear America,” a zone from Mexico south through Peru, where the major crops of maize, beans, and squashes were domesticated, pottery was invented, monumental architecture developed, and the most elaborate arts and political empires created. “Nuclear America” nevertheless remains a useful concept. The history of Mexico is as relevant to United States indigenous histories as that of Rome is to the histories of European nations beyond Italy. The earliest direct evidence for agriculture in the Americas is fragments of squash left in a rockshelter overlooking the Oaxaca Valley in southwest Mexico, 8000 bce. No wild varieties of this squash grow in Oaxaca; it was probably taken to Oaxaca from farther north in Mexico, presumably to eat its seeds, possibly to use the shell as container. Olmec, second half of the second millennium bce, began Mexican architectural styles as well as sculpture and full-scale maize agriculture.