Although Italy was a member of the Triple Alliance, it did not join Germany and Austria-Hungary when the conflict started in 1914, arguing that the war had been initiated by the two Central Powers and that the Triple Alliance was a defensive pact. Italians protested for the lack of consultation before Austria issued the ultimatum to Serbia and invoked a clause of the Triple Alliance, according to which both Italy and Austria-Hungary were interested in the Balkans and whoever changed the status quo in the region had to compensate the other; Austria-Hungary refused to give compensations before the end of the war. In May 1915, after secret parallel negotiations with both sides, the Italians entered the war as one of the Allied Powers, hoping to acquire the Italian-speaking "irredent lands" of Trento and Trieste (in Italian discourse the conflict was described as the "fourth war of independence" against Austria) and other territories (German-speaking South Tyrol, the largely Slavic-speaking regions of Istria and Dalmatia where Italians lived in coastal cities, some colonial compensations) promised them by the allies in the 1915 treaty of London.
Italy opened a front against Austria-Hungary along the Eastern Alps and the Isonzo river. Fighting was marked by trench warfare and attrition. On the Julian sector, the Italian army launched numerous offensives and made several conquests (most significantly Gorizia in 1916 and Bainsizza in 1917), but both sides suffered heavy casualties. On the Asiago plateau, in 1916, an Austrian offensive was followed by an Italian counter-offensive. Italy was forced to retreat in 1917 by a German-Austrian offensive at the Battle of Caporetto, when the Central Powers were able to move reinforcements to the Italian Front from the Eastern Front.
Further offensives by the Central Powers were stopped by Italy at Monte Grappa in November-December 1917 and on the Piave River in June-July 1918. On 24 October 1918, the anniversary of Caporetto, Italy launched the battle of Vittorio Veneto: Italian troops achieved a breakthrough, recovered the territory previously lost, and moved into Trento and Trieste by the time fighting ended on November 4 (a date celebrated as National Unity Day in Italy). The centuries-old Habsburg Empire collapsed. Italian armed forces were also involved in the Western Front (taking part in the Second Battle of the Marne, around Bligny, and in the subsequent Hundred Days Offensive), the African theatre, the Balkan theatre and the Middle Eastern theatre.
At the end of World War I, in the Paris Peace Conference of 1919, Italy was recognized a permanent seat in the League of Nations' executive council and the possession of many promised territories: Trento and Trieste, whose annexation completed national unification, South Tyrol, Istria and some colonial compensations. Territories in Dalmatia (although also included in the 1915 treaty of London) and the town of Fiume (despite a sizeable Italian population) were not assigned to Italy as they were claimed by Yugoslavia; a part of Italian nationalists (the followers of Gabriele D'Annunzio) accused the Allies of "mutilating" the Italian victory and occupied Fiume without royal assent. The quarrel between Italy and Yugoslavia would be solved by the treaty of Rapallo (1920), with Italy annexing the Dalmatian capital of Zara and Fiume becoming a free State. The post-war period saw increasing political violence, eventually leading to the establishment of Mussolini's Fascist government in 1922.
From neutrality to intervention
Italy was a member of the Triple Alliance with Germany and Austria-Hungary. Despite this, in the years before the war, Italy had enhanced its diplomatic relationships with the United Kingdom and France. This was because the Italian government had grown convinced that support of Austria (the traditional enemy of Italy during the 19th century Risorgimento) would not gain Italy the territories it wanted: Trieste, Istria, Zara and Dalmatia, all Austrian possessions. In fact, a secret agreement signed with France in 1902 sharply conflicted with Italy's membership in the Triple Alliance.
A few days after the outbreak of the war, on 3 August 1914, the government, led by the conservative Antonio Salandra, declared that Italy would not commit its troops, maintaining that the Triple Alliance had only a defensive stance and Austria-Hungary had been the aggressor. Thereafter Salandra and the minister of Foreign Affairs, Sidney Sonnino, began to probe which side would grant the best reward for Italy's entrance in the war or its neutrality. Although the majority of the cabinet (including former Prime Minister Giovanni Giolitti) was firmly against intervention, numerous intellectuals, including Socialists such as Ivanoe Bonomi, Leonida Bissolati, and, after 18 October 1914, Benito Mussolini, declared in favour of intervention, which was then mostly supported by the Nationalist and the Liberal parties. Pro-interventionist socialists believed that, once that weapons had been distributed to the people, they could have transformed the war into a revolution. Italy's neutrality also favored Spain's neutrality.La desconocida razón por la que España evitó de milagro entrar en la Primera Guerra Mundial, ABC (10/10/2018)
The negotiation with Central Powers to keep Italy neutral failed: after victory Italy was to get Trentino but not South Tyrol, part of the Austrian Littoral but not Trieste, maybe Tunisia but only after the end of the war while Italy wanted them immediately. The negotiation with the Allies led to the London Pact (26 April 1915), signed by Sonnino without the approval of the Italian Parliament. According to the Pact, after victory Italy was to get Trentino and the South Tyrol up to the Brenner Pass, the entire Austrian Littoral (with Trieste), Gorizia and Gradisca (Eastern Friuli) and Istria (but without Fiume), parts of western Carniola (Idrija and Ilirska Bistrica) and north-western Dalmatia with Zara and most of the islands, but without Split. Other agreements concerned the sovereignty of the port of Valona, the province of Antalya in Turkey and part of the German colonies in Africa.
On 3 May 1915 Italy officially revoked the Triple Alliance. In the following days Giolitti and the neutralist majority of the Parliament opposed declaring war, while nationalist crowds demonstrated in public areas for it. (The nationalist poet Gabriele D'Annunzio called this period le radiose giornate di Maggio—"the sunny days of May"; also called the Radiosomaggismo.) Giolitti had the support of the majority of Italian parliament so on 13 May Salandra offered his resignation to King Victor Emmanuel III, but then Giolitti learned that the London Pact was already signed: fearful of a conflict between the Crown and the Parliament and the consequences on both internal stability and foreign relationships, Giolitti accepted the fait accompli, declined to succeed as prime minister and Salandra's resignation was not accepted. On 23 May, Italy declared war on Austria-Hungary. This was followed by declarations of war on the Ottoman Empire (21 August 1915, following an ultimatum of 3 August), Bulgaria (19 October 1915) and the German Empire (28 August 1916).United States Department of State, Declarations of War and Severances of Relations (1914–1918) (Washington, DC: Government Printing Office, 1919).
Italy entered into World War I also with the aim of completing national unity with the annexation of Trentino-Alto Adige and Julian March: for this reason, the Italian intervention in the First World War is also considered the Fourth Italian War of Independence, in a historiographical perspective that identifies in the latter the conclusion of the unification of Italy, whose military actions began during the revolutions of 1848 with the First Italian War of Independence.
Italian Front
Topography
The Italian Front stretched from the Stelvio Pass (at the border triangle between Italy, Austria-Hungary and Switzerland) along the Tyrolean, Carinthian, and Littoral borders to the Isonzo. Its total length was around , of which ran in high alpine terrain.Helmut Peter, Das Wesen des Hochgebirgskrieges 1915–1917/1918. phil. Dipl., Wien 1997 (masch.), p. 6. This information relates to measurements as the crow flies. Taking into account the natural terrain, the many yokes, peaks and ridges with the resulting differences in height, the effective length was several thousand kilometers.Jordan, Krieg, p. 88; Schaumann/Schubert, Süd-West-Front, S. 21.
The front touched very different geographical areas: in the first three sections - from the Stelvio Pass to the Julian Alps in the area of Tarvisio, it ran through mountainous territory, where the average ridge heights reached 2,700 to 3,200 meters. The higher mountainous regions have a highly rugged relief with little vegetation; Elevations over 2,500 meters are also covered by glaciers. The barren landscape and lack of sufficient arable land led to little development of these high elevations; settlement was largely limited to the lower-lying zones. From the Julian Alps to the Adriatic Sea, the mountains are constantly losing on height and only rarely reach 1,000 meters as in the area around Gorizia. This area is also sparsely populated and characterized by a harsh climate with cold winters and very hot and dry summers. A craggy karst landscape spreads out around the Isonzo valley, which adjoins the Italian foothills of the Alps in the southwest.Jordan, Krieg, p. 89
The topographical characteristics of the front area had a concrete impact on the conduct of the war. The rocky ground, for example, made it difficult to dig trenches and in addition, the karst rock in the Isonzo Valley turned out to be an additional danger for the soldiers. If grenades exploded on the porous surface fragments of the exploding rock acted as additional shrapnel.
Mobilization
Archduke Eugen, who was already in command of the Balkan forces, was promoted to Generaloberst on May 22, 1915 and was given supreme command of the new southwest front.Rauchensteiner, Doppeladler; S. 244, Etschmann, Südfront, p. 27. Together with his chief of staff Alfred Krauß the 5th Army was reorganized and placed under the command of General d. Inf. Svetozar Boroević who on May 27 had arrived from the Eastern Front. The K. u. k. Landesverteidigungskommando in Tyrol (LVK) was handed to GdK Viktor Dankl to protect the Tyrolean borders. It included the German Alpenkorps which was suitable for operations in the high mountains, the first divisions arrived on May 26; a short time later, the Alpenkorps was already taking part in combat operations against Italian units, although the German Empire was not officially at war with Italy until August 28, 1916.Etschmann, Südfront, p. 27, p. 29 f. The "Armeegruppe Rohr" stood under the command of Franz Rohr von Denta and was to secure the Carinthian front. The transfer of the 5th Army and additional troops from the east went smoothly; within a few weeks, Archduke Eugen had around 225,000 soldiers under his command. In June the 48. Division (FML Theodor Gabriel) and finally, in July, the four Kaiserjäger regiments and three k.k. Landesschützen regiments from Galicia were added. A major advantage of the Austro-Hungarian defense was its entrenchment on higher ground.
Italy ordered general mobilization on May 22, 1915 and by the end of June four armies had marched into the north-east border area. In the deployment plan of the Italian general staff (Commando Supremo) under the direction of FM Luigi Cadorna, three main points were set:
The 1st Army was to encircle the Tyrolean front from the west and south. The 4th Army was to set up position in the Cadore and Carnia The 2nd and 3rd Armies, on the other hand, were opposed to the 5th k.u.k. Army, in the Julian Alps and on the Isonzo.