The Franco-Prussian War (1870-1871) was the final conflict in Bismarck's plan for German unification.

The cause was the growing rivalry between an ambitious Prussia and a nervous France under Napoleon III.

The immediate trigger was a dispute over a Prussian prince's candidacy for the vacant Spanish throne.

Bismarck deliberately edited and published a telegram, the 'Ems Dispatch,' to make it seem as if the Prussian king had insulted the French ambassador.

This provocation enraged French public opinion and led France to declare war on Prussia.

As Bismarck had predicted, the French declaration of war caused the independent southern German states to ally with Prussia out of nationalist sentiment.

The Prussian-led German forces were better prepared and organized, winning a series of swift victories.

The decisive moment was the Battle of Sedan, where Napoleon III himself was captured along with his entire army.

The war led to the fall of the Second French Empire and the proclamation of the German Empire.

France was forced to cede the territories of Alsace and Lorraine to Germany, which created lasting resentment.