After the events in 1914, Sonnino was initially supportive to the side of the old allies of the Triple Alliance, Germany and Austria-Hungary. He firmly believed that Italian self-interest entailed participation in the war, with its prospect of Italian territorial gains as a completion of Italian unification. However, after becoming Minister of Foreign Affairs in November 1914 in the conservative government of Antonio Salandra and realizing that it was unlikely to secure Austro-Hungarian agreement to the concession of certain Austro-Hungarian territories to Italy, he sided with the Entente powers – France, Great Britain and Russia – and sanctioned the secret Treaty of London in April 1915 to fulfill Italy’s irrendentist claims. Italy consequently declared war on Austria-Hungary on May 23, 1915.