When the First World War began, Italy was a second-order European power, allied to Germany and Austria-Hungary through the Triple Alliance of 1882. While Italy had no serious differences with Germany – indeed, she formally renewed the Triple Alliance in 1912 – she had irredentist claims stretching back to the 1860s to the Italian-speaking Austro-Hungarian region of Trentino/ South Tyrol which soured the Triple Alliance. Italy also claimed Istria and Trieste (citing the presence of Italian speakers) and wanted the Dodecanese islands, occupied in 1912, to be recognised as Italian. The differences with Austria-Hungary meant that Italy remained neutral in 1914. Italian socialists and pacifists opposed the war, and she was militarily weak; she had a largely agrarian economy, a shortage of raw materials (especially coal), deep internal social divisions, a weak army and a disinterested population. So, on 2 August 1914, the Italian government seized on the lack of consultation by the Central Powers formally to declare its neutrality, a decision that surprised no one.
When the early campaigns of the war proved indecisive, the Italian government, led by Prime Minister Antonio Salandra, slowly shifted its allegiance towards the Entente. This was evident in the movement of Italian troops from the border with France to the one with Austria-Hungary over the winter of 1914-15. Italy’s king, Victor Emmanuel III, Salandra and Foreign Minister, Baron Sidney Sonnino, were the driving forces in the move to war, supported by an eclectic grouping of political and cultural revolutionaries including the radical journalist Benito Mussolini, the nationalist writer Gabriele D’Annunzio and the Futurist artist Filippo Marinetti (who thought that war would help to modernise Italy). The Italian population divided into those who supported neutrality, those keen on intervention and those uninterested in war. The government, meanwhile, accelerated its military build-up and, fearful of Austro-Hungarian expansion into Albania, occupied the Albanian port of Valona (Vlöre).
Salandra’s talk of Italy’s national interests – or sacro egoismo – along with the actions of his interventionist foreign minister Sonnino, made an accommodation with Austria-Hungary difficult. The conservative Sonnino, committed to Italian colonial expansion, was sure that prolonged neutrality would wreck Italy’s chances of post-war territorial gains. While at first Sonnino was keen on siding with Germany, its check on the western front made him re-assess the situation and seek to support whichever side looked like winning. Thus, Sonnino had discussions with both sides in late 1914 and early 1915, but Italy’s territorial irridenta made any settlement with the Central Powers highly unlikely.
By December 1914, Salandra stated publicly Italy’s opposition to the Central Powers’ war aims and to Austro-Hungarian expansion in the Balkans. In response, Germany sent her former chancellor Bernhard von Bülow with a powerful diplomatic mission to build contacts with noninterventionist politicians. In early 1915, von Bülow and the Austrian ambassador to Italy tried to satisfy Sonnino’s demands for Italian territorial expansion in the Balkans and South Tyrol. They made some progress, but Germany was unable to get Vienna to offer the Italians territory in South Tyrol, Trieste and Albania. Austria-Hungary’s formal rejection of Italian demands in April 1915 opened the door for Entente diplomacy, with the advantage that the Entente powers could offer Austro-Hungarian land to Italy. Moreover, with the Central powers heavily engaged in the war, the reversal of the Triple Alliance seemed like an attractive and risk-free operation for Italy.
On 26 April 1915, Italy signed the Treaty of London with Britain, France and Russia. In return for Italy joining the war, the London pact accepted Italian territorial claims in Europe and Asia Minor, and promised extensive military and economic aid for Italy. Italy would get reparations, the Trentino/South Tyrol region, Trieste, Istria, the Dalmatian/ Adriatic coast (excepting the port city of Rijeka/Fiume) and parts of southern Turkey around Adalia. With the exception of South Tyrol, Trieste and Istria, these areas contained very few if any Italians. Italy’s far-ranging territorial claims would cause problems after the war with some Entente politicians arguing that they had offered too much territory in the rush to sign Italy up for the war. When the Bolsheviks published the secret territorial provisions of the Treaty of London, it caused an outcry in Greece and Serbia, whose territory had been promised to Italy, and from those inside Italy opposed to what they saw as an expansionist, unnecessary war.
In May 1915, as war approached there were orchestrated pro-war demonstrations. On 13 May 1915, parliamentary opposition to the war led to the resignation of Salandra’s cabinet. Three days later the King re-instated Salandra when it was found impossible to appoint a neutralist administration. Salandra’s re-appointment gave him the mandate for war and, although 74 left-wing deputies opposed war, the Italian army was mobilised and war declared against Austria-Hungary on 23 May 1915 (Italy did not declare war against Germany until 1916). Once in the war, military policy passed almost entirely to the Chief of Staff, Luigi Cadorna, who led the Italian army from 1915 to 1917 on eleven costly and disastrous offensives against Austria-Hungary along the river Isonzo. Italy’s lacklustre military performance in the war adversely affected her post-war efforts to secure all of the territorial demands of the Treaty of London and she finished the war feeling that she had been short-changed territorially.