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How did Austria trigger the war of 1859 against Piedmont?

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Unification of Italy — unification of Italy The unification of Italy. The dates are those of annexation, first to Sardinia-Piedmont and after 1861 to the Kingdom of Italy.

To trigger the war of 1859, the Count di Cavour sought to provoke Austria into an act of aggression that would activate a secret military alliance with France.21

Following secret negotiations at Plombières in 1858, Cavour and Napoleon III planned to expel Austrian forces from the Italian peninsula. To ensure France would honor its commitment, Cavour needed to make Austria appear as the aggressor.21

The situation escalated when Austrian military leaders urged Emperor Francis Joseph to declare war on Piedmont. On April 23, 1859, Austria issued an insulting and unacceptable ultimatum demanding that Piedmont demobilize its troops. Piedmont rejected these terms, and Austria declared war three days later, fulfilling Cavour’s strategic goal of drawing France into the conflict on the side of the Piedmontese.12