It shows how the US economy has devolved from dependency on agriculture. The Blueish Green areas represent, at the county level, that dependency in 1950 and 2000 (that is the latest date).
Observation: In the earlier time period agricultural interests and affects spread to far more people in rural areas. Lets say it was more democratic in nature. This served as a counter-weight to the shifting power bases to/in urban areas.
Fast-forward to today. The politics of agriculture affect fewer people (nominally) and corporate interests have replaced the democratic nature of rural politics.
Policies of the bygone era had to appeal to tens of thousands of small business owners (farmers) with varied interests. Today they have to only appeal to a concentrated number of large corporate farms with homogeneous interests.
|Image via Big Picture Agriculture from a report by the Kansas City Federal Reserve Bank|