I like the point that you make Vera, about agriculture working well for the Egyptians. It plays into the discussion really well. They are a great example of how civilizations start. Also, it can show you how agriculture could be less destructive, if used in places like the Nile Delta, and if limited to not full-time agriculturalists. The problem with agriculture is more then just the soil depletion though. Population dynamics play a large role in agriculture's destructiveness. Because agriculture creates an easy-to-store food source, and because it is very fragile, agriculturalists have insane amounts of food storage. I know lots of horticulturalists did this too. I've read the Iroquois had 7 years of food stored at any time for example. I think that food storage, like agriculture, is a slippery slope of population growth problems. Depending on your region, some cultures could not survive without food storage or caches. The problem with agriculture is that it promotes grain storage specifically. Also, grain calories increase fertility. Agriculture, or rather, full time agriculture creates an artificially inflated population. "artificially inflated" meaning, beyond sustainable carrying capacity. Its a short term population increase, followed by a collapse. So when a population, like the Babylonians for example, begin to crash, they take what is a less destructive to the land practice like river basin agriculture and move it outside of its origins to a place where it does not "work". It's like Asian civilizations doing the same thing with rice paddies. They build damns to flood areas to create more rice paddies. But it's not a replenishing flood like a river flowing out of a mountain range, so it doesn't replenish the soil. This is why we have to use Petroleum as fertilizer; this replicates what the river would have done.
Taking agriculture out of the river basin was inevitable in a way. When the population crashed, rather then recognizing that it doesn't work full time, the exported the practice out of the river in an attempt to curb the population crash. This is why Stanley Diamond said, "Forests precede us, deserts dog our heels." We're recreating a flood plain or field or river delta, where there is none. This creates an exponential growth problem of population and deforestation.
Let's talk about Horticulture. The Natives of the Northwest had ridiculously large populations for "hunter-gatherers". Anthropologists says this is because there were so many salmon here and the population didn't have to do much or move. So you had sedentary cultures of hunter-gatherer-fishermen. This isn't exactly true. They lived here for 10,000 years or so. They relied heavily on Western Red Cedar for their daily survival. Cedar is not a food source. When we think of "increase in food production" or managing the land for "food production" we often do not hear about all the other forms of life that are not direct food, but are used in the production of food. For example, Cedar canoes were taken out for fishing. Cedar boxes stored food. Cedar bark was used to make baskets to collect food. Cedar wood was used to make all of their longhouses. Cedar is a late comer in terms of succession in the Northwest; a cedar forest is the climax of succession here. Old growth Cedars today pale in comparison to what the white people were clear-cutting 200 years ago. We're talking about trees that were over 2000 years old. These trees were so large and so old that the natives here harvested wood out of them in a way that didn't kill the trees. In a very real sense, they tended these forests and perhaps even created them with routine fire maintenance. If your objective is growing old growth forests of Cedar, you're not going to destroy the soil from under yourself; you're going to build it. "Forest gardening", "Permaculture" or "Horiticulture" are example of subsistence strategies that are heavily engaged in land management in a way the builds soil and biomass. It might mean more people in dense areas, and that leads to more social problems, but not environmental ones.
I really recommend these three books:
Tending the Wild by M. Kat Anderson
The Earth's Blanket by Nancy Turner
Keeping it Living (edited by Nancy Turner)
They basically cover how this is accomplished.