The Franco-Prussian War (1870-1871) was a war fought between France and Prussia. It was started by Emperor Napoleon III of France, but quickly resulted in a Prussian invasion and defeat of French forces at the Battle of Sedan, resulting in the capture of the Emperor himself. The French continued to fight for several more months but eventually surrendered.
Prussia united with several other German states and became the German Empire, with Kaiser Wilhelm I as monarch and Otto von Bismarck as chancellor. Alsace-Lorraine, a border territory, was transferred to Germany.
A socialist revolution broke out in France and the Paris Commune was formed. This was eventually suppressed by troops loyal to the government who invaded Paris from the countryside.
Emile Zola wrote an excellent novel, The Debacle, about this war.