Completed the following sentence: In 1859, France sided with the Kingdom of Sardinia in a war against Austria, the Austro-Sardinian War. Napoléon III n'a pas tenu sa promesse à Cavour de se battre jusqu'à ce que tout le Royaume de Lombardie-Venetia ait été conquis. <unk> <unk> <unk>
Magenta and Solferino, both French victories, Napoleon thought the war too costly to continue and made a separate peace behind Cavour's back in which only Lombardy would be ceded.