Changes

The evolution of American football has been varied. Key influences were likely Greco-Roman games that left their mark in Europe. With the Medieval Period, those games emerged to form the beginnings of what would become rugby and soccer (or football). However, within that were the origins of American football. In the United States, it was concern over safety that led to rules that shaped what became American football and how it differed from its European counterparts (i.e., rugby and soccer). The formalization of rules and social events such as war (e.g., World War I) further shaped the sport. The rapid expansion of popularity in the early 20th century eventually led to professional teams, which served as the foundation of the modern NFL. Along the wayafter the founding of the NFL, rules were refined, often influenced by the medium of television.