French and Prussian animosity
French and Prussian animosity have been swelling in the background since the German Wars of Unification started in the 1860s. The French Duc de Gramont hopes that a victory over Prussia could restore French prestige while Prussian Chancellor Bismarck needs a reason to fulfill his dream of German unification from above. When the crisis about the Spanish throne escalates with the Ems Dispatch, the die is cast and the Franco-Prussian War begins.
Credit to : Real Time History