Mesoamerican trading networks extended into southwestern North America, where by 300 B.C.E. the Hohokam people and other groups were using irrigation canals, dams, and terraces to enhance their farming of arid lands (Map 11.2). Like the Olmecs and other Mesoamerican peoples, the Hohokam built ceremonial platforms and played games with rubber balls that were traded over a long distance in return for turquoise and other precious stones. Along with trade goods came religious ideas, including the belief in local divinities who created, preserved, and destroyed. Desert peoples planted crops such as agave, as well as cotton and maize that came from Mexico. Other groups, including the Anasazi (ah-nah-SAH-zee), the Yuma, and later the Pueblo and Hopi also built settlements in this area using large sandstone blocks and masonry to construct thick-walled houses that offered protection from the heat. Eventually drought, deforestation, and soil erosion led to decline in both the Hohokam and Anasazi cultures.

To the east, the Mississippian culture also engaged in monumental mound building beginning around 2000 B.C.E. One of the most important mound-building cultures was the Hopewell (200 B.C.E.–600 C.E.), named for a town in Ohio near the site of the most extensive mounds. Some mounds were burial chambers. Other mounds formed animal or geometric figures. Hopewell earthworks also included canals that enabled trading networks to expand, bringing products from the Caribbean far into the interior. Those trading networks also carried maize, allowing more intensive agriculture to spread throughout the eastern woodlands of North America.

At Cahokia (kuh-HOE-kee-uh), near the confluence of the Mississippi and Missouri Rivers in Illinois, archaeologists have uncovered the largest mound of all, part of a ceremonial center and city that housed perhaps thirty-eight thousand people. Work on this complex of mounds, plazas, and houses began about 1050 C.E. and was completed about 1250 C.E. The largest mound rose in four stages to a height of one hundred feet and was nearly one thousand feet long. On its top stood a large building, used perhaps as a temple.

Cahokia engaged in long-distance trade reaching far across North America and became a highly stratified society. Mississippian mound builders relied on agriculture to support their complex cultures, and by the time Cahokia was built, maize agriculture had spread to the Atlantic coast. Particularly along riverbanks and the coastline, fields of maize, beans, and squash surrounded large, permanent villages containing many houses, all encompassed by walls made of earth and timber.