The following is an excerpt from Future Scenarios: How Communities Can Adapt to Peak Oil and Climate Change  by David Holmgren. It has been adapted for the web.
The broad processes of human history can be understood using an ecological framework that recognizes primary energy sources as the strongest factors determining the general structure of human economy, politics, and culture. The transition from a hunter-gatherer way of life to that of settled agriculture made possible the expansion of human numbers, denser settlement patterns, and surplus resources. Those surplus resources were the foundations for what we call civilization, including the development of more advanced technologies, cities, social class structures, standing armies, and written language. Archaeology records a series of civilizations that rose and fell as they depleted their bioregional resource base.
Lower-density simple agrarian and hunter-gatherer cultures took over the territory of collapsed civilizations and allowed the resources of forests, soils, and water to regenerate. That, in turn, gave rise to new cycles of growth in cultural complexity.
In the European Renaissance, the medieval systems that evolved from the remnants of the Roman Empire were re-infused with knowledge and culture from the Islamic and Asian civilizations and grew into competing nation-states. A combination of the demands of internal growth and warfare between nations almost exhausted the carrying capacity of Europe. As this ecological crisis deepened in the fourteenth and fifteenth centuries, European exploration in search of new resources carried the “diseases of crowding” around the world. In the Americas, up to 90 percent of many populations died, leaving vast resources to plunder. Starting with the plundering of precious metals and seeds of valuable crop plants such as corn and potatoes, European nations soon moved on to building empires powered by slavery that allowed them to exploit and colonize the new lands well stocked with timber, animals, and fertile soils, all rejuvenating in the wake of the collapse of indigenous populations.
European population, culture (especially capitalism), and technology then grew strong enough to tap vast stocks of novel energy that were useless to previous simpler societies. European coal fueled the Industrial Revolution while food and other basic commodities from colonies helped solve the limits to food production in Europe. As industrialization spread in North America and later in Russia, oil quickly surpassed coal as the most valuable energy source, and accelerated the jump in human population from one billion in 1800 to two billion in 1930 to now over six billion in one lifetime. This massive growth in human carrying capacity has been made possible by the consumption of vast stocks of nonrenewable resources (in addition to expanding demand on the renewable biological resources of the planet). Rapid rates of urbanization and migration, technology change, increasing affluence, and disparity of wealth as well as unprecedented conflicts between global and regional powers have accompanied this transition.
The history of the twentieth century makes more sense when interpreted primarily as the struggle for control of oil rather than the clash of ideologies. In emphasizing the primacy of energy resources I am not saying that the great struggles between ideologies have not been important in shaping history, especially capitalism and socialism, but most teaching and understanding of history underestimates the importance of energetic, ecological, and economic factors.
The fact that conflict has increased as available resources have expanded is hard to explain using conventional thinking. One way to understand this is using older moral concepts about more power leading to greater moral degradation. Another equally useful way to understand this is using ecological thinking. When resources are minimal and diffuse, energy spent by one human group, tribe, or nation to capture those resources can be greater than what is gained. As resources become more concentrated (by grain agriculture, for example, and even more dramatically by tapping fossil fuels), the resources captured through diplomacy, trade, and even war are often much greater than the effort expended.
The final phase in the fossil-fuel saga is playing out now as the transition from oil to natural gas and lower-quality oil resources accelerates, with massive new infrastructure developments around the world as well as increasing tension and active conflicts over resources. We can only hope that nations and humanity as a whole learn quickly that using resources to capture resources will yield less return and incur escalating costs and risks in a world of depleting and diffuse energy.