Starting in the 1840s, German immigration had resulted in a huge waves of immigrants into the country. A immigration backlash occurred, and politicians had considerable concerns about divided loyalties with the single largest ethnic group in the United States (roughly 8% IIRC). At this time it was very common for there to be german languages schools, businesses and Churches. What held these groups together was actually the german language. Many of the immigrants had left before the creation of the formal german state, others fled the failed revolution in 1848 or the foundation of the german state, while others were Reichsdeutsche (imperial germans, who had left Germany after the unification) or Volksdeutsche (people who spoke german, but were outside of the borders of Germany). These groups had different political point of views, and complex relationships with the fatherland, and this heterogeneous background identified with the German Kultur, but not always the german political state.

In the run up to world war I, many of these German groups pushed for a total munitions ban, but even before the United States formally entered the war, German agents began acts of sabotage - most notably the Black Tom Island incident. This played into a massive anti-german backlash during the next election (where both candidates attacked "hyphenated americans"). Once the war began, German nationals were arrested and outlawed, and german language schools, churches and societies made easy targets. States outlawed german language institutions. German churches and institutions switched to english, and never went back.

In the aftermath of the war, the great depression, and then world war II, what few german institutions in the US pretty much died off, leaving a situation where 17% of Americans self-identify as German-American, but where that really has meaning other then the random ancestry.com profile.