The conflict centered on Prussian ambitions to extend German unification. Prussian chancellor Otto von Bismarck planned to provoke a French attack in order to draw the southern German states—Baden, Württemberg, Bavaria and Hesse-Darmstadt—into an alliance with the Prussian-dominated North German Confederation.
Bismarck adroitly created a diplomatic crisis over the succession to the Spanish throne, then rewrote a dispatch about a meeting between King William of Prussia and the French foreign minister, to make it appear that the French had been insulted. The French press and parliament demanded a war, which the generals of Napoleon III assured him that France would win.
.. French determination to regain Alsace-Lorraine and fear of another Franco-German war, along with British concern over the balance of power, became factors in the causes of World War I.