(a re-statement of my earlier points without the unnecessary soapboxing--my apologies to the AskHistorians mods.)

I'm not an Americanist, so this will remain a 'holding' point until the Americanists arrive, but: There were intensive efforts to eradicate German language and/or culture during and immediately after the First World War.

In May of 1918, for instance, the Governor of Iowa issued the 'Babel' Proclamation, stating that "only English is legal in public or private schools, in public conversations, on trains, over the telephone, at all meetings, and in all religious services." Similarly, in June of 1918, South Dakota made it illegal to 'use' (speak) German at any public gathering.

Nebraska removed German-language books from schools in 1918, and forced the closure of German-language newspapers. They even made it illegal to teach in any foreign language.

But during the war, the informal attacks on German were much more threatening: American self-styled patriots even went on Dachshund killing-sprees, if you can believe it. German town and street-names were re-named. (Berlin, Ohio changed its name to Fort Loramie, Ohio.) German families changed their name, German breweries changed their brand-name, etc.

Some words of German origin were changed, at least temporarily. (Sauerkraut came to be called "liberty cabbage"; hamburgers became "liberty sandwiches"; and so forth).

Anti-German legislation only intensified after war's end, curiously. Indiana, for instance, made it illegal to teach the German language in Indiana in 1919. Ultimately, anti-German-speaking laws were struck down by the Supreme Court in 1923. (Meyer v. Nebraska; Oliver Wendell Holmes dissented.)

There's been a ton written on this (most of which I've not read myself, sorry!): but one book that leaps to mind is Christopher Capozzola's Uncle Sam Wants You; he talks about anti-German activities for 10 pages or so.