Origin of Wheat Flour as we know it today actually was in the second decade of the 20th century. Prior to that date the only wheat grown was soft shelled wheat and the type of flour produced was typically what we would consider stone ground whole wheat. At that time a rust blight basically decimated the US wheat crop for more than two years in a row. Essentially, soft shelled wheat could no longer be easily grown in the US. Farmers switched to hard shelled wheat, which is immune to the blight but millers quickly found that the hard shell gave a very different flavor and texture to the wheat. The steel roller method of milling was then deployed to create a product which more closely approximated the soft shelled wheat flour of a few years earlier. Later on millers tried to sell whole wheat flour as such, successfully.
This switch from soft to hard shelled wheat was one of the causes of the "dust bowl" of the 1920's as the demands of hardshelled wheat on the soil were significantly different than soft shelled wheat.