The Second Italian War of Independence, also called the Austro-Sardinian War or Austro-Piedmontese War, was fought by the Second French Empire and the Kingdom of Sardinia against the Austrian Empire in 1859 and was a key event in the process of Italian unification.
The Piedmontese, following their defeat to Austria in the First Italian War of Independence, found that they could not defeat a great power such as Austria without allies. This led Camillo Benso, conte di Cavour to attempt to establish relations with other European powers, partially through Piedmont's participation in the Crimean War. In the peace conference at Paris for the Crimean War, Cavour attempted to bring attention to efforts for Italian unification. He found Britain and France to be sympathetic, but entirely unwilling to go against Austrian wishes, as any movement towards Italian independence would necessarily threaten Austria's territory in Lombardy and Venetia. Individual talks between Napoleon III and Cavour after the conference identified Napoleon as the most likely, albeit still uncommitted, candidate for aiding Italy.
On January 14, 1858, Felice Orsini, an Italian, led an attempt on Napoleon III's life. This assassination attempt brought widespread sympathy for the Italian unification effort, and had a profound effect on Napoleon himself, who now was determined to help Piedmont against Austria in order to end the revolutionary activities that the governments inside Italy might allow to happen in the future. Emperor Napoleon III and Camillo Benso, Conte di Cavour, the prime minister of the Kingdom of Piedmont-Sardinia, signed a secret treaty of alliance against Austria: France would help Sardinia to fight against Austria if attacked, and Sardinia would then give Nice and Savoy to France in return. This secret alliance served both countries: it helped with the Sardinian (Piedmontese) plan of unification of the Italian peninsula under the House of Savoy, and weakened Austria, a fiery adversary of Napoleon III's French Empire.