Regarding the conflation of different nationalities (Dutch, Swiss,
Belgian, etc.) as "German" in the U.S.:

The problem of German identity is further complicated by the fact that
Germany really didn't exist as a modern nation-state until the German
Empire was proclaimed at the end of the Franco-Prussian War in 1871.  Of
course, there were earlier confederations, and certainly a belief among
nationalists that there was a German "nation" in the cultural sense.

This fact became very apparent to me while researching Virginia military
companies from Richmond in the CSA army.  Unlike the census, the
enlistment records noted the soldier's place of birth as the
principality or city he was from, not "Germany."  How regional
identification, religious differences, and other factors affected the
formation of German-American identity is an interesting question.

Gregg Kimball
Library of Virginia