The U.S. enter the War.

When the United States got involved in WWI, one third of the army was foreign born and immigrants as children, and over 10 million american citizens came from the Nations of the Central Power.  Millions of Irish Americans sided with The Central Power as well, due to their hatred for the English.

After the U.S. entered the war, in the name of patriotism, musicians stopped playing Bach and Beethoven, American renamed sauerkraut "Liberty Cabbage", schools stopped teaching the German language, and German newspapers were shut down. These things all occurred because of the high rise of searching for German Spies in our Nation.  Even if you didn't purchase war bonds, you were treated harshly, as it was considered unpatriotic. Even street names that had to do with anything German were renamed, such as Berlin Avenue in St. Louis was changed to Pershing.