The Midwest is one of the best major areas in the world when it comes to large scale farming. There are several natural factors that contribute to the Midwest having very good characteristics for farming.
The region's climate is mostly semi-arid. The precipitation levels are relatively low and they only occur seasonally. The summers are hot and dry, the winters are cold and snowy, while the spring and autumn are mild and more rainy.
The region comes to be in a a somewhat rain-shadow from both sides, with mountain ranges blocking the influences from the oceans.
The whole area is valley-like, and it has relatively low elevation.
Naturally, this region has been covered by grasses, which are actually the main factor that provided enormous amounts of biomass, making the soil very deep and fertile.
The area doesn't have forests, which is good for the plants because it enables the winds to blow freely, which is always great for the plants in order to not catch diseases, and to have proper aeration.