later POD
#1 Simple as that: the Boxer rebellion, 1901.
#2 Thesis on Alsace-Lorraine: IMHO, the main point would have been to treat the Alsatians better. For far too long, Alsace-Lorraine had been administered by Berlin and the military. Incidents like the Saverne-affair showed that many Germans didn't accept the Alsatians as equally German.
The French nation would have gotten over it- somewhen. Although later than over the incident of the coronation in Versailles. Yes, it was a humiliation, but so was the burning of the White House in 1812.
#3 Nevertheless, in retrospective, it probably needs a devastating major war between France and Germany after 1871 to shake them enough to find to each other. How about a WW1 with monarchy in Germany surviving despite the defeat and signing Locarno? Not turning into the 3rd Reich, Germany and France might find more common ground which could gradually turn into an alliance. I just cannot see anyone insane enough to attack France AND Germany.
#4 Less probable - France being forced into a German-dominated "Mitteleuropa" after its defeat in 1916. Still angry about the treacherous Brits, who left them alone in 1914 and chose to profiteer from the continental war to an obscene degree, French collaborateurs stand staunchly on Germany's side when it comes to the fight for Global Domination agains the Anglo-Americans in the 1920s.
In every city there are still streets named after the battles of Sedan and Wissembourg. As a new nation it needed like the US national symbols to create a feeling of unity.
Tomorrow I will go and look for a Sedanstrasse in Dorsten, where I live (80,000 inhabitants) and in Münster where I work (260,000 inhabitants).