The Franco-Prussian War was the most important conflict that was fought in Europe after the Napoleonic wars and before the First World War, and ended with the complete victory of Prussia and its allies.
Explanation:
The Franco-Prussian War was fought between July 19, 1870 and May 10, 1871 between the Second French Empire (and after the fall of the regime, by the Third French Republic) and the Kingdom of Prussia, with the support of the North German Confederation and the allied kingdoms of Baden, Bavaria and Württemberg. The conflict marked the outbreak of tension between the two powers, which increased after the failure of Napoleon III's project to annex Luxembourg, an event that caused the end of a relatively balanced relationship with Otto von Bismarck's Prussia. The tension became greater due to the increasing influence, not tolerated by France, exercised by the German states in the south of the Main river, and the Prussian leadership exercised within the North German Confederation (state created in 1867 after the victory of Prussia in the Austro-Prussian War).
The most important consequence of the Prussian victory was the creation of the German Empire, which maintained a very influential role in the international political relations of the following decades. The French debacle also brought the end of the Second Empire of Napoleon III and, with the fall of it, the temporary subordination of the role of France in comparison with the other powers of European families. The end of the imperial era in France marked the beginning of the Third French Republic, which - in size and influence - became the most important republican regime among those then existing on the continent.