It was not Orsini's attack of January 14, 1858 that influenced Napoleon III on the question of Italian unification. A former carbonaro, the victory of his armies in the Crimea gave him the stature necessary to accomplish this mission which was close to his heart. Napoleon III allies himself with Piedmont-Sardinia, a reunifying power. He married his cousin to Clothilde, the daughter of the King of Piedmont in January 1859. In July 1858, a secret agreement was signed with Cavour in Plombières. The sympathy of all Europe was with Italy, shared for centuries among so many masters; the Russia of Alexander II of Russia won since an interview in Stuttgart by the generosity of the Emperor rather than by armed force, offered no opposition to this act of justice while the United Kingdom, a liberal force, applauded. In France, business circles and Christians are reluctant.
When Austria declared war on Piedmont in May 1859, France got involved. Napoleon III took the lead of the army and won the victories of Magenta and Solferino on June 4 and 24, 1859, but at the cost of heavy losses. The prospect of an Austro-Prussian alliance in the war stopped Napoleon III, who signed the Peace of Villafranca in July 1859. The Austrian presence in Italy was maintained. The Italians are furious because they could not complete the reunification. Under the Plombières agreement, France receives the county of Nice and Savoy, attached after plebiscite in April 1860.