In the lead up to WWI, the federal and state governments basically told the various German speaking synods (and a few German Catholic churches) to speak in English, or else. That “or else” meant your church got burnt down, or you ended up in jail, or some locals came in the middle of the night and made sure you understood your “duty” as an American. My grandfather was a 10 year old boy in 1918, and remembered when they suddenly had to speak in English at church, put the US flag on the altar steps, and other things to prove that their loyalty wasn't to Germany. Never mind that most of them left Germany because of the religious madness that the Prussians were imposing at the time.
Pres. Wilson would not accept anyone who didn't tow the party line. There were people who were jailed for not saluting the flag (because of religious reasons they could not). Anytime I hear someone talking of “repression of freedoms” during the war on terror, I just point them to a few history books on WWI to give them a little perspective.
Things were a bit tense in WWII, but by that time most of the German immigrants had assimilated very well.
Thanks.