German-Americans were interned in WWII, but not on a broad blanket ethnic basis. If you were affiliated with the German-American Bundt, American Nazi Party, or other organs of the Reich, you were definitely in for some scrutiny and possible internment for the duration.
I believe there were Italian Americans interned as well.
Note that the sheer numbers of German and Italian ethnics would have made large-scale internment impossible. Ethnic Japanese were a small enough minority to be manageable.
I don't know of any Germans put into camps in World War II. Captured German soldiers, yes, but German American civilians? I've never heard of it before.
Another story entirely.