I digress. Back to serious geographic material.
The agricultural core has strong physical geography. Its formation strongly reflects the agriculture, much like it does in the Pacific northwest. There is a "longitudinal"divide in the agricultural region which I believe gives it a sense of balance. On the Easter side, rainfall dominates and provides certain crops. On the Western side, it is dryer, the region takes a break from the high water carrying capacity of the land. These influences relate to that of the PNW in a sense: there are dry regions as well as wet regions. While scattered in the PNW, they are laterally side-by-side in these region of the Midwest.
Its continentality keeps up with its strong seasonal range. There is little risk of drought.
Agriculture is lucratively possible thanks to its little-hilly terrain. The flat land also does for good water drainage. There are also visible results of glaciation.
REGION SIMILARITY ALERT
The soils involved in the Midwest are what makes the crops flourish. Alfisols and mollisols. It just so happens that its the mollisols themselves that also dominate the PNW's soil type! Mollisols are superbly suited for grain production (such as corn in the state of Idaho). The soil is formed under grasses, most likely as a result to stay moist and rich in nutrients. Organic content is high, and its A-horizon goes as deep as 5 ft. All of these facts demonstrate the importance of the Core region. The nutrient richness of the soil types provide crop growth. A lucrative and important aspect to both US regions (Core and PNW).
Wheat and meat are another important development in the Core. Wheat is a year-round, reliable good where shipping and break-in points determine wheat distribution. Meat is from the livestock. As livestock feeds off the grains and wheat, it makes for domestick livestock. Hogs and pigs seem to dominate a large part of the Core region.
While such regions may not be too populated or urbanized, it is also regions such as these where it is best that urbanization stays at bay. The space and fields are needed to feed the entire United States.