Papal rule was briefly interrupted by the Roman Republic, which was established in 1798 under the influence of the French Revolution. The Congress of Vienna instituted new states throughout Italy after the fall of Napoleon’s Empire. These were the Kingdom of the Two Sicilies, the restored Papal States and King Charles-Albert’s Piedmont-Sardinia. Another Roman Republic was established in 1849 in the wake of the cross-continental anti-monarchy movements of 1848. Giuseppe Garibaldi was the most influential figure of the Italian unification. His aims were supported by the sly Camille Cavour, Prime Minister of Piedmont-Sardinia. Cavour launched wide-scale industrialisation in his effort to unite Northern Italy. He sent the army of Piedmont-Sardinia to fight alongside the British and French in the Crimean War. He established cordial relations between France and Piedmont-Sardinia, which he was to exploit in the future.

With the return of the pope to Rome, the city was excluded from the unification process, a key element in the second Italian war of independence. Garibaldi invaded Sicily with little resistance and captured it. Publicly, Cavour denounced the revolutionary’s act, but he had provided military assistance to him in secret. After that, Garibaldi crossed the Strait of Messuna and captured the entire kingdom. Cavour’s alliance with France motivated him to plan an attack against Venetia and Lombardy. French and Italian forces agreed to capture the two states, but the French pulled out of the agreement shortly thereafter. At this time, only Venetia had been captured. Cavour was enraged and resigned. Later, he was reappointed.

During the Austro-Prussian War, Italy and Prussia agreed that Italy would attack Austria in exchange for Lombardy. The Prussians were victorious, and the northern front of Italy became complete. The Franco-Prussian War broke out in 1870. Napoleon III could no longer defend the Papal States. The Italian army entered Rome that same year. The Kingdom of Italy then annexed Rome and Latium. The Italian government offered to let the pope retain authority over Leonine City, but the pope refused because he believed that he would be affirming the legitimacy of the Italian kingdom's rule over his former territory. The pope declared himself a prisoner in the Vatican. Finally, Rome became the capital of Italy in 1871.