London Pact (Italian: Patto di Londra), or more correctly, the Treaty of London, 1915, was a secret pact between the Triple Entente and the Kingdom of Italy. The treaty was signed in London on 26 April 1915 by the United Kingdom of Great Britain and Ireland, the French Third Republic, the Russian Empire, and the Kingdom of Italy. Its intent was to gain the alliance of Italy against its former allies, including German empire and Austro-Hungary. The main lure was promising large swaths of Austria-Hungary to the north of Italy and to the east across the Adriatic. Britain also promised funding. Italy promised to enter the war the next month. The Allies could easily outbid Austria-Hungary and thereby won a military alliance with 36 million Italians. The secret provisions were published by the Bolsheviks when they came to power in Russia in late 1917.
The First World War (1914–1918) was an unexpected development that forced Italy to decide whether to honor the alliance with Germany and Austria. For six months Italy remained neutral, saying that the Triple Alliance was only for defensive purposes. Italy took the initiative in entering the war in spring 1915, despite strong popular and elite sentiment in favor of neutrality. Italy was a large, poor country whose political system was chaotic, its finances were heavily strained, and its army was very poorly prepared. The Triple Alliance meant little either to Italians or Austrians – Vienna had declared war on Serbia without consulting Rome. Two men, Prime Minister Antonio Salandra and Foreign Minister Sidney Sonnino made all the decisions, as was typical in Italian foreign policy. They operated in secret, enlisting the king later on, but keeping military and political leaders entirely in the dark. They negotiated with both sides for the best deal, and got one from the Entente, which was quite willing to promise large slices of the Austro-Hungarian Empire, including the Tyrol and Trieste. Russia vetoed giving Italy Dalmatia and Albania. Britain was willing to pay to get 36 million Italians as new allies who threatened the southern flank of Austria.