Until about 1850, human cultivation, overall, increased the nutrient quality of the soil in fertile areas, and kept it about the same or increased it in marginal areas. Occasionally, that would crash, and famine and plague would reduce the human population, giving the soil a chance to recover naturally.
However, modern, powered farming methods and the reliance on unbalanced artificial fertilizers, starting in about 1850, changed all that. The Dust Bowl was one major result - topsoil developed over thousands of years was wiped away in less than a decade. Another example is in India: Traditional farming practices increased fertile topsoil for 5,000 years until it was over a yard (meter) deep. But modern agriculture since the 1960s has wiped away a couple of feet already. India may suddenly face a dust bowl and mass starvation in the near future.
Our foods are becoming measurably less nutritious. Naturally or organically grown products on naturally rich soil delivered locally are much better. This is the health and ecological basis of organic food and local food movements.