It has certainly been the received wisdom all my life that Germany was dangerously nationalistic during WWII, thus discrediting nationalism per se in the minds of many. Reading Chesterton's description of German attitudes and philosophy during WWI provides powerful evidence for the theory that the two wars were a single war, won incompletely by the Allies by their own fault in 1919, and thus fought again in 1939.
The suggestion under discussion is broadly this: that Germany suffers from an overdose and debauch of national feeling, and that therefore Nationalism, which has destroyed our enemies, must be watched with a wary eye even in our friends and in ourselves, as if it were a highly dubious explosive.The obvious had not occurred to me, meaning that my apprenticeship will have to continue. England has a nationalism extending back centuries, as does France, Russia, Italy, Poland, Spain, Switzerland...
There have been border changes and dominant provinces, certainly - Castille, Anjou - but a sense of greater nationality extending far into the past. Only Germany was a late-comer, and like a young athlete or entertainer newly rich, became drunk with sudden wealth. Its nationalism was never about its boundaries or inhabitants anyway, but about Teutonism, Das Volk, the race. It seeped across borders to include Germanish people in Austria and Czechoslovakia. It sought to include the English and Scandinavians as lesser partners. But it excluded many people actually in Germany itself: Jews, Gypsies, Poles.
I suspect that nationalism became unfashionable not because of Germany, but because it interfered with the spread of communism.