Modern nation-states appeared in the wake of the French Revolution, with the formation of patriotic sentiments for the first time in Spain during the Peninsula War (1808–1813, known in Spain as the Independence War). Despite the restoration of the previous order with the 1815 Congress of Vienna, the "nationalities question" became the main problem of Europe during the Industrial Era, leading in particular to the 1848 Revolutions, the Italian unification completed during the 1871 Franco-Prussian War, which itself culminated in the proclamation of the German Empire in the Hall of Mirrors in the Palace of Versailles, thus achieving the German unification.