Answer:
The answer is: letter C, Franco-Prussian War
Step-by-step explanation:
Napoleon III (1848-1852) was France's first President. He founded the Second French Empire. His downfall was mainly due to the "Franco-Prussian War" which occurred in 1870.
The Franco-Prussian War was marked by the defeat of many French armies by the Germans due to the former's chaotic mobilization. During the war, Napoleon III was already very ill, thus it was hard for him to defeat the Germans who were very much overwhelming in number. It was during the "Battle of Worth" that many French soldiers were killed and captured. The news reached Prime Minister Ollivier in Paris, thus they immediately planned on what to do next. The decision for the army's movement was actually a secret, but it was published in France's newspaper. This reached the Germans who were then able to make a more strategic way to win. Napoleon III was captured and became a prisoner of war.
This then resulted to the giving of Alsace-Lorrain Territory to Germany, which marked the German empire as a newly unified territory after defeating France.