Troops back from Great War. Popularity grows with the home run and glamour of the profession. Athletes as celebrities. Soccer was by and for the working man, and often the only entertainment available. National identity tied to soccer.
Diplomatic relations break off.
Capitalism used to break color barrier for blacks in main-stream sports. Racial pride at stake for African Americans and Germans. 11th Olympics in Berlin. Carefully orchestrated by Nazis for propaganda. Athletes as soldiers.