America enforced "100% Americanism" during World War I by repressing German culture at this time.
For example, Americans changed the names of popular German foods in order to be more "American." During the war, many people referred to hamburgers as "liberty sandwiches" and sauerkraut as "liberty cabbage." Americans went as far as calling German measles "liberty measles."
These three examples show that the US tried to suppress German culture as much as possible during World War I.