In the early stages of the 20th century infectious diseases were characterized by a theory known as the germ theory with the focus on one single disease at a time (McLeroy & Crump, 1994). Most of the focus of disease prevention was trying to figure out what was the leading cause of death during that time, especially in the early 1900s. Chronic diseases was considered the leading cause of death (McLeroy & Crump, 1994). The epidemiologic transition was the main interest in health promotion and disease prevention in the United States during this time. This transition had three stages that determined the major diseases and helped find new ways of health promotion. This was how the historical evolution began to promote health and prevent diseases
