The Italian state grew out of the kingdom of Sardinia-Piedmont, where in 1848 King Charles Albert introduced a constitution that remained the basic law, of his kingdom and later of Italy, for nearly 100 years. It provided for a bicameral parliament with a cabinet appointed by the king. After World War II, on June 2, 1946, the Italians voted in a referendum to replace the monarchy with a republic. A Constituent Assembly worked out a new constitution, which came into force on January 1, 1948.

Source: Britannica