Article: The Nazis, led by Adolf Hitler, attempted to unite all the people they claimed were "Germans" (Volksdeutsche) into one realm, including ethnic Germans in eastern Europe, many of whom had emigrated more than one hundred fifty years before and developed separate cultures in their new lands. This idea was initially welcomed by many ethnic Germans in Sudetenland, Austria, Poland, Danzig and western Lithuania, particularly the Germans from Klaipeda (Memel). The Swiss resisted the idea. They had viewed themselves as a distinctly separate nation since the Peace of Westphalia of 1648.

Question: Since when had the Swiss viewed themselves as a different nation?
1648