In the early 1900s, various medical practices such as chiropractic, osteopathy, homeopathy, and traditional medicine coexisted in the United States. However, a significant event occurred in the period between 1915 and 1920 that would change the landscape of medicine in the country for years to come: the Flexner Report.

The Flexner Report was funded by the Carnegie Corporation and compiled by Abraham Flexner. Flexner traveled across the United States by stagecoach, train, and horseback (before the interstate highway system was in place) to visit and evaluate medical schools that used drugs in their practices. After completing his inventory, Flexner presented the findings to the Carnegie Corporation, which had a financial interest in drug companies.

As a result of the Flexner Report, the Carnegie Corporation and the Rockefellers provided millions of dollars in funding to the medical schools and hospitals identified in the report. This marked the beginning of the dominance of traditional medicine, as other medical practices were marginalized.

Today, most people in the United States are unaware of this history of the evolution of medicine.