Will our warmer future also be more violent? In this lecture, Dagomar Degroot of Georgetown University surveys the cooler past to find some answers. First, he explains what we know about the "Little Ice Age," a climatic regime that lasted from 1450 to 1850, and was cooled by volcanic eruptions and low solar activity. Then, he argues that the weather of the Little Ice Age helped cause and decide wars within and between different societies. Finally, he shows why some societies were more vulnerable to the destabilizing influence of climate change than others, and offers lessons for the coming century.