Richard Heinberg writes at Common Dreams:
History is often made by strong personalities wielding bold new political, economic, or religious doctrines. Yet any serious effort to understand how and why societies change requires examination not just of leaders and ideas, but also of environmental circumstances. The ecological context (climate, weather, and the presence or absence of water, good soil, and other resources) may either present or foreclose opportunities for those wanting to shake up the social world. This suggests that if you want to change society—or are interested in aiding or evaluating the efforts of others to do so—some understanding of exactly how environmental circumstances affect such efforts could be extremely helpful.