Dirt: The Erosion of Civilizations

The top layer of "dirt" is what helps our civilizations survive. Many great empires have died after a thousand years due in part to their destruction of this topsoil. Darwin dedicated his final career work to the exploration of topsoil production and the important role that worms played in producing more soil. The early book spends a great deal of time discussing different civilizations and the impact they had on the topsoil. Soil degradation is viewed as a significant reason for the rise and fall of empires. As populations grow, irrigation and other large scale works are needed to help support overfarmed soils. This leads to creation of government structures. Further growth leads to farming of marginal lands and erosion. Vast empires are needed to provide food for the urban areas. Eventually, the degradation puts the society on the edge, and a small climatic change or weather anomaly can push the society over the edge. "Empire" food production can lead to events like the Irish Potato famine. Many people in Ireland starved due to the potato crop failure. Meanwhile, cattle were being exported from Ireland to England.
The author does a great job of making his point. He uses simple math to show that intensive agriculture results in a rate of soil erosion that limits most civilizations to primary lifespan of about 1000 years. Some can last longer if they are blessed with renewable soil (like the Nile River), or can extend their farming reach. However, without care to the soil, they will fall. Soil is a tricky resource because the benefits of conservation often don't occur until the following generation. It is very hard to get political buy in for the short term sacrifices needed for long term gain.
While the ideas in the book are good, the writing is not. The chapters are organized by topic, but they ramble on, jumping around from example to example somewhat haphazardly. The point could be made in a book a fraction of the size. The ideas are strong enough to encourage making it through the book in spite of the poor organization.