Italy would switch sides in 1915 .whom did this hurt

It  Hurt to Germany and the Austro - Hungarian  Empire .

The Treaty of London, also known as the Treaty of London (in English) or Patto di Londra (in Italian), was signed in London on April 26, 1915. For him, Italy entered the First World War on the side of the Entente . The treaty was secret and the signatory countries were: The Kingdom of Italy, United Kingdom of Great Britain and Ireland, France and the Russian Empire. Under the treaty, Italy would receive the areas inhabited by Italians in the Austro-Hungarian Empire, much of the Dalmatian coast and the rest of the Balkan territories of the Austro-Hungarian Empire would be divided between three independent States: the Kingdom of Serbia, the Kingdom of Montenegro and Croatia .

In return, Italy was committed to abandon the Triple Alliance, which united the German and Austro-Hungarian empires and enter the war on the side of the Entente. The change of side had already been agreed at the beginning of September of 1914 in a secret agreement signed in London. The entry into the war had to take place in less than a month after the signing of the treaty and this was done; the declaration of Italian war was announced on May 23. The application of the treaty was very much conditioned by the dissolution of the Austro-Hungarian Empire and the emergence of new nations, especially Yugoslavia, which were not willing to accept the concessions promised to Italy by the Entente, and by the entry into the war of the United States, which defined new war aims and refused to admit the delivery of territories of Slavic majority to Italy.