"<span>The North opposed the idea that a state could leave the Union, but the South supported it" is the best option from the list but all this had to do with the issue of slavery. </span>
All German Americans were required to join military armed forces. To those who hadn't signed up, were imprisoned.
But apparently, in many sources, it states that German-Americans in both Germany and US, were imprisoned. Sad truth :(
It decreased due to the fact that many jobs were opening in the urban areas so people left their farms and houses in rural areas to get a job in a bigger city.