A rapidly increasing number of historians in the past few decades have become aware of the importance of the natural environment to human history, and have created a new set of interpretive tools within history. As a subject, environmental history is the study of how human beings and human societies have related to the natural world through time. As a method, it is the use of ecological analysis as a means of understanding human history. Environmental historians recognize the ways in which the living and non-living systems of the earth have influenced the course of human affairs. They also evaluate the impacts of changes caused by human agency in the natural environment. They think, or at least most of them do, that the idea of environment as something separate from the human, and offering merely a setting for human history, is misleading. Instead, whatever humans have done to the rest of the earth has inevitably affected themselves. The living connections of humans to the ecosystems of which they are part must be integral to the historical account. Humans operate within the principles of ecology, and must continue to do so as long as the species is to survive. That all human societies, everywhere and throughout history, have existed within and depended upon biotic communities is true of huge cities as well as small farming villages and hunter clans. The connectedness of life is a fact.