For all Nationalism you'd have to go back pretty far, however to delay most of it a century you'd need to prevent the French Revolution which gave rise to alot of turmoil throughout Europe both directly (Napoleon) and indirectly (other powers going to war with Rev. France to strangle the idea of the Republic) and prevent something similar for most of the 19th century.
Having said that Nationalism as a major thing would probably develop in other places before then AND it would probably look different, that is we may instead of seeing German Nationalism, see Bavarian and Prussian Nationalism etc.