WWI was not the result of nationalism. That was the pretext for leaders eager for the “glory” of war.
WWI was a textbook example of the dangers of intertwined alliances.
It seemed more like countries so worried that other countries were gonna strike first that they @#$$ed up big time and got in a war no one wanted.
It was the result of nationalism, or a sort of it.
It would not have happened had there been no German empire. This was created as a result of a pan-German romantic ideal based on ethnic identity, which had not previously existed. Before then people owed loyalty to a ruler, on of the dozens of small principalities that made up Germany, and their own particular sort of German, a “little” nationalism not a great one. If it all had remained that way there would have been no Great War.
This applied to the other participants too. France had run a century or more of patriotic propaganda and language standardization to truly create France. Russia was drawn to the war at least partly as a result of its own public opinion, at the time besotted by pan-slavism. Italy was still half mad with the absurdity of irredentism.
Etc. The rule is little nationalisms=little wars. Great nationalisms=great wars.
“WWI was not the result of nationalism. That was the pretext for leaders eager for the glory of war.”
It was really no more and no less a stick up of the existing order by the Germans. Glory had nothing to do with it at the highest levels.