This article advocates for broadening social science history to include an even larger horizon, to reach a new level of understanding of human society in the past. It builds on and shares insights from 20 years of research that integrates environmental knowledge and environmental science into a history of social change, while trying to understand in detail how people changed the environment. The focus of the research is the demographic, social, agricultural, and environmental history of the US Great Plains, from the 1870s to the end of the twentieth century. Beyond supporting the argument for a broader interdisciplinary vision of history, the article shows how the Great Plains environment was changed by human action, and the ways that the environment shaped human behavior in turn. The history of the plains shows that the impact of human action on the land was dramatic and unmistakable. People radically changed land cover, but their actions were only one factor in causing events like the Dust Bowl, and only one part of the measurable increase in greenhouse gases. At the same time, the environment also constrained and shaped human behavior, even though it had less to do with family organization than broad trends in social change in the late nineteenth and early twentieth centuries. The environment’s most dramatic contribution was to spur out-migration in the 1930s when drought caused widespread agricultural failure, further confirmation of the importance of going beyond purely social factors to understand how people lived in the past.