April 9 - The Austrian army in Italy mobilizes against Piedmont.
April 23 - The Austrians send an ultimatum to Piedmont, demanding demobilization. This puts Austria in the position of an aggressor, and leads to French intervention. Piedmont rejects the ultimatum, and war breaks out.
July 11 - Austrian Emperor Franz Joseph, faced with an expensive war against France and the Kingdom of Sardinia and potential revolution in Hungary, meets Napoleon III, who also worries at the costs of extending the war and fears the effects of Italian nationalism, at Villafranca. By the preliminary treaty signed there, hostilities cease. Lombardy is ceded to the French (who immediately cede it to Sardinia), while the Austrians keep Venetia and the French promise to restore the Central Italian rulers expelled in the course of the war. This brings the Austro-Sardinian War effectively to a close.