Final answer:
Count Camillo di Cavour, the Sardinian prime minister, was the architect of Italian unification, leveraging alliances and military victories to unify Italy under King Victor Emanuel II by 1870.
Step-by-step explanation:
The Sardinian prime minister who plotted and carried out plans for Italian unification was Count Camillo di Cavour. Appointed as Prime Minister in 1852, Cavour was the mastermind behind the Risorgimento, the movement for the unification of Italy. Aiming to increase the power of Piedmont-Sardinia, he utilized Italian nationalism and strategic alliances to achieve this goal.
Cavour's intelligent leadership and political maneuvers included forming an alliance with French emperor Napoleon III. Through their combined military efforts, they provoked and won a war against the Austrian Empire in 1859, leading to Piedmont's acquisition of Lombardy and other northern Italian states. Despite his contempt for the south, Cavour's annexation efforts eventually extended to include these regions as well, shaping a unified Italy under the monarchy of Victor Emanuel II.
Although the unification process had its downfalls, particularly for southern Italy which faced increased taxes and economic challenges, the legacy of Italian unification remained significant. It brought together disparate Italian states under one national identity, a process that was fully realized when Rome was annexed in 1870.