The document summarizes Joseph Tainter's theory from his book "The Collapse of Complex Societies" that societies like the Romans, Maya, and inhabitants of Chaco canyon collapsed due to becoming overly complex. Tainter argues that early on, increasing complexity provides marginal benefits to societies, but it eventually reaches a point of diminishing returns where the costs outweigh the benefits. When unexpected stresses occur, highly complex societies lack flexibility and collapse. The document relates this theory to complex modern societies.