Sonnino, Sidney, Barone (bärôˈnā sōn-nēˈnō) [key], 1847–1922, Italian foreign minister instrumental in Italy's entry into World War I. A member of the diplomatic corps (1867–73), he later became interested in social and economic problems, particularly in the conditions of the peasants, and founded an economic review, later converted into a political daily. Sonnino entered parliament in 1880 and as minister of finance (1893–96) under Crispi took drastic measures and succeeded in balancing the budget. Perhaps the most important conservative leader after the fall of Antonio Starrabba Rudinì (1898), he was the chief rival of Giovanni Giolitti in the prewar period. He was twice briefly premier (1906, 1909–10). As foreign minister during World War I, he negotiated (1915) the secret Treaty of London, by which Italy entered the war on the Allied side in exchange for promises of vast territorial gains. The opposition of President Wilson to the fulfillment of the secret treaty caused major difficulties at the Paris Peace Conference of 1919, where Sonnino represented Italy with Vittorio Emanuele Orlando. Sonnino retired from politics in 1919.