23rd May
On 23 May 1915, Italy declared war on Austria-Hungary and entered the First World War on the side of Britain, France and Russia. It was a dramatic decision because Italy had once been allied with Austria-Hungary and Germany through the Triple Alliance. Yet when war broke out in 1914, Italy stayed neutral, arguing that the alliance was defensive and that Austria-Hungary had started the crisis by attacking Serbia. This gave Italy time to watch events unfold and, more importantly, to decide which side might offer the greatest reward.
Italy and Austria-Hungary had never been comfortable allies. Many Italians still saw Austria as the old enemy from the wars of Italian unification. Austria-Hungary controlled territories that Italian nationalists believed should belong to Italy, including Trentino, Trieste, South Tyrol and parts of the Adriatic coast. These lands were often described as Italia irredenta, meaning “unredeemed Italy”. To nationalists, Italy’s unification was not complete while Italian-speaking communities remained under Habsburg rule.
During its months of neutrality, Italy negotiated with both sides. Austria-Hungary tried to keep Italy out of the war, but it was unwilling to surrender enough territory to satisfy Italian ambitions. The Allies were prepared to offer more. They wanted Italy to open a new front against Austria-Hungary, forcing the Central Powers to divide their armies and resources. For Britain, France and Russia, Italian intervention would put extra pressure on an empire already fighting in the east and the Balkans.
The decisive agreement was the secret Treaty of London, signed on 26 April 1915. Italy promised to join the Allies within a month. In return, it was promised major territorial gains if the Allies won the war. These included Trentino, South Tyrol up to the Brenner Pass, Trieste, Istria, parts of Dalmatia and several Adriatic islands. The Italian public did not know the full details at the time, because the treaty was secret. The decision was made by a small group of leaders who believed the war could complete Italy’s national ambitions and raise its status as a great power.
Inside Italy, the move toward war caused a bitter political struggle. Prime Minister Antonio Salandra and Foreign Minister Sidney Sonnino supported intervention, as did King Victor Emmanuel III. Many members of parliament, however, were opposed. The former Prime Minister Giovanni Giolitti believed Italy could gain concessions from Austria-Hungary without fighting. Socialists, many Catholics and much of the rural population also opposed the war. They feared the cost in lives, money and hardship.
On the other side were the interventionists. They included nationalists, some liberals, students, intellectuals and public figures who believed war would make Italy stronger. The poet Gabriele D’Annunzio gave emotional speeches urging Italians to support intervention. Benito Mussolini, who had broken with the Socialist Party over the issue, also argued in favour of war. At this stage Mussolini was not yet the dictator he would later become, but the intervention crisis helped shape his move toward aggressive nationalism.
In May 1915, pro-war demonstrations filled the streets in what interventionists called the “Radiant Days of May”. The phrase suggested national excitement and unity, but Italy was far from united. Many people remained doubtful or opposed. Even so, the interventionists were loud, organised and influential. When Salandra briefly resigned, the king refused to replace him with Giolitti and instead backed the government’s pro-war policy. This helped clear the final obstacle to intervention.
On 23 May 1915, Italy formally declared war on Austria-Hungary. The declaration came into effect the next day, 24 May, when Italian troops began operations along the frontier. One interesting detail is that Italy did not declare war on Germany at the same time. Although Germany and Austria-Hungary were close allies, Italy’s first declaration was aimed only at Austria-Hungary. Italy did not declare war on Germany until 28 August 1916.
The Italian army entered the war with confidence, but it faced enormous difficulties. Its commander-in-chief, General Luigi Cadorna, believed in strict discipline and repeated offensive attacks. The army was large, but it lacked enough heavy artillery, modern equipment and experience of industrial warfare. The landscape made the task even harder. The frontier ran through mountains, valleys, rivers and fortified positions. This was not a simple march into enemy territory; it was a campaign fought across some of the harshest terrain in Europe.
Much of the fighting centred on the Isonzo River in the northeast, near the border with modern Slovenia. Cadorna launched repeated attacks there in the hope of breaking through towards Trieste. These battles became known as the Battles of the Isonzo. They were costly and exhausting, with Italian troops often attacking uphill against strong Austro-Hungarian defences. Gains were usually small, and casualties were heavy.
Elsewhere, the war reached high into the Alps. Soldiers fought among snow, ice, rock and glaciers, sometimes at extraordinary altitudes. Avalanches, frostbite and exposure could be as deadly as shells and bullets. Both sides carved tunnels into mountains, built cableways to move supplies and placed artillery in positions that seemed almost impossible to reach. The Italian Front became a war not only between armies, but against the landscape itself.
Italy’s entry forced Austria-Hungary to defend yet another front. The empire was already under strain from fighting Russia and Serbia, so the new Italian Front added pressure to its armies and resources. Even so, Austro-Hungarian forces used the mountains well and often held strong defensive positions. The war Italy had hoped might bring swift success turned instead into a long struggle of attrition.
For ordinary Italian soldiers and civilians, the cost was severe. Many soldiers came from poor rural areas and had little connection with the nationalist dreams that had taken Italy into the war. Families at home faced shortages, rising prices and grief as casualty lists grew. The strict discipline of Cadorna’s army also left a bitter memory, especially because punishments could be harsh and morale was often fragile.
The greatest crisis came in October 1917 at Caporetto, when Austro-Hungarian and German forces broke through the Italian lines. The retreat was chaotic and devastating, but Italy did not collapse. Cadorna was replaced by General Armando Diaz, who treated the army more carefully and rebuilt its strength. Italian forces stabilised the front along the Piave River and, in 1918, won a decisive victory at Vittorio Veneto. Soon after, Austria-Hungary began to fall apart.
Italy finished the war among the victors, but the peace did not bring complete satisfaction. It gained important territories such as Trentino, South Tyrol, Trieste and Istria, but not everything promised in the Treaty of London. Nationalists complained that Italy had won a “mutilated victory”, a phrase that later became powerful in post-war politics. The disappointment and anger after the war helped create the atmosphere in which Fascism grew.
