Modern milling of grains in the mid 19th century, allowed manufacturers to separate the parts of the whole grain and use only the starchy endosperm to create an inexpensive and very finely ground white flour.  Before this, grains were ground in whole form and the flour contained the bran and germ as well as the starch.  Without these, refined flours will last longer on the shelf but they contained much lower levels of nutrients and so manufacturers “enrich” wheat and other grain flours with synthetic nutrients.