After this war, France had to give to Prussia some regions under its control. These regions were Alsace and the German language speaking Lorraine. After this war, Prussia took steps to unite independent German states into one country, the German Empire. The historical term for this is the Unification of Germany.
The causes of the Franco-Prussian War are mostly due to France being nervous of a Protestant country on their border. While France had helped Prussia beat Austria in the Austro-Prussian War (1866), France would not let the North and South German states unify. In 1869, the throne of Spain was offered to a Catholic branch of the Prussian royal family. Otto von Bismarck, the Chancellor of Prussia, wanted them to accept the offer, as this would make France weaker diplomatically without a war.
France found out about the offer, and demanded that Prussia reject it, since France did not want two Prussia-backed states on her borders. The Southern German states were angry at this, and Bismark provoked a war with France in 1870. Napoleon III thought it was necessary to attack Prussia because this was a part of his plan to conquer Europe like his predecessor Napoleon I.