aid Italy although he was still uncommitted. On 14 January 1858, Felice Orsini, an Italian, led an attempt on Napoleon III's life. The assassination attempt brought widespread sympathy for the Italian unity and had a profound effect on Napoleon III himself, who now was determined to help Piedmont against Austria to defuse the wider revolutionary activities, which governments in Italy might later allow to happen. After a covert meeting at Plombières on 21 July 1858, Napoleon III and Cavour on 28 January 1859 signed a secret treaty of alliance against Austria. France would help Sardinia-Piedmont, if attacked, to fight against Austria if Sardinia-Piedmont gave Nice and Savoy to France in return. The secret alliance served both countries by helping with the Sardinian-Piedmontese plan of unification of the Italian Peninsula under the House of Savoy. It also weakened Austria, a fiery adversary of Napoleon III's French Second Empire. Cavour, being unable to get French help unless the Austrians attacked first, provoked Vienna by a series of military maneuvers close to the border. Sardinia mobilised its army on 9 March 1859. Austria mobilised on 9 April 1859 and issued an ultimatum on 23 April demanding the complete demobilisation of the Sardinian Army. When it was not heeded, Austria started a war against Sardinia on 26 April. The first French troops entered Piedmont on 25 April, and France declared war on Austria on 3 May. Forces The French Army for the Italian campaign had 170,000 soldiers, 2,000 horsemen and 312 guns, half of the whole French army. The army, under the command of Napoleon III, divided into five corps: the I Corps, led by Achille Baraguey d'Hilliers; the II Corps, led by Patrice de MacMahon; the III Corps, led by François Certain de Canrobert, the IV Corps; led by Adolphe Niel, and the V Corps, led by prince Napoléon Joseph Charles Paul Bonaparte. The Imperial Guard was commanded by Auguste Regnaud de Saint-Jean d'Angély. Napoleon III participated in the war and showed up on the battlefield in the belief that it would motivate the French people during the war. That would prove successful. The Sardinian Army had about 70,000 soldiers, 4,000 horsemen and 90 guns. It was divided into five divisions, led by Castelbrugo, Manfredo Fanti, Giovanni Durando, Enrico Cialdini and Domenico Cucchiari. Two volunteer formations, the Cacciatori delle Alpi and the Cacciatori degli Appennini, were also present. It was led by Victor