The conflict began in 1848 when the Kingdom of Sardinia (so called because the island, in spite of being basically a colony, provided the Piedmontese House of Savoy with the title of king) declared war on Austria, while most of its cities - especially Milan, Venice and Vienna - were in revolt. The Sardinians had limited support from the other major Italian states (the Grand Duchy of Tuscany, the Kingdom of the Two Sicilies and the Papal States). Initially, the Italian allies succeeded in capturing Milan, but the Sardinian King's (at the time Carlo Alberto) ambiguous attitude, coupled with his fear of losing the Kingdom's sovereignty, led to the dissolution of the alliance. The Austrians counterattacked and defeated the Sardinians at Custoza in July 1848 and reclaimed Lombardy, concluding an armistice. The following year Carlo Alberto denounced the armistice and attacked, but was quickly outmanouvered by Austrian feldmarshall Joseph Radetzky and decisively defeated at Novara.
The war ended with the Kingdom of Sardinia paying an indemnity to Austria and Carlo Alberto abdicating in favour of his son.
That defeat confirmed that the Kingdom of Sardinia could not defeat the Austrians without an equally powerful ally. With the support of their Prime Minister - Camillo Benso, Conte di Cavour - the Italians found an ally in Napoleon III, who signed a secret alliance. Cavour proceeded to provoke Austria with a series of military manoeuvers near the border, which sparked a war in April 1859 when an ultimatum to demobilise went unheeded.
The war's notable high point was the Battle of Solferino in June 1859, where a combined Franco-Sardinian Army, led by Napoleon III and the Sardinian King Vittorio Emanuele II, fought the Austrian Army led by Emperor Franz Josef; that was considered the largest battle since the Battle of Leipzig (with both sides fielding roughly 160,000 troops each). The Franco-Italian Army defeated the Austrians, however, fearful that more German states would involve themselves in the war, Napoleon agreed to an armistice and Sardinia was awarded Lombardy in the ensuing Armistice of Villafranca. The following year, with French and British approval, Sardinia annexed Parma, Modena, Tuscany and the Papal Legations as part of Cavour's absurdly audacious plan to conquer the Two Sicilies, whereas France was given Nice and Savoy as payment for their support in the war.