Triple Alliance (1882) in the context of "Splendid isolation"

The July Crisis was a series of interrelated diplomatic and military escalations among the major powers of Europe in mid-1914, which led to the outbreak of World War I. It began on 28 June 1914 when the Bosnian Serb nationalist Gavrilo Princip assassinated Archduke Franz Ferdinand, heir presumptive to the Austro-Hungarian throne, and his wife Sophie, Duchess of Hohenberg. A complex web of alliances, coupled with the miscalculations of numerous political and military leaders (who either regarded war as in their best interests, or felt that a general war would not occur), resulted in an outbreak of hostilities amongst most of the major European states by early August 1914.

Following the murder, Austria-Hungary sought to inflict a military blow on Serbia, to demonstrate its own strength and to dampen Serbian support for Yugoslav nationalism, viewing it as a threat to the unity of its multi-national empire. However, Vienna, wary of the reaction of Russia (a major supporter of Serbia), sought a guarantee from its ally, Germany, that Berlin would support Austria in any conflict. Germany guaranteed its support through what came to be known as the "blank cheque", but urged Austria-Hungary to attack quickly to localise the war and avoid drawing in Russia. However, Austro-Hungarian leaders would deliberate into mid-July before deciding to give Serbia a harsh ultimatum, and would not attack without a full mobilisation of the army. In the meantime, France met with Russia, reaffirmed their alliance, and agreed they would support Serbia against Austria-Hungary in the event of a war.

The Kingdom of Italy (Italian: Regno d'Italia, pronounced [ˈreɲɲo diˈtaːlja]) was a unitary state that existed from 17 March 1861, when Victor Emmanuel II of Sardinia was proclaimed King of Italy, until 10 June 1946, when the monarchy was abolished, following civil discontent that led to an institutional referendum on 2 June 1946. This resulted in a modern Italian Republic. The kingdom was established through the unification of several states over a decades-long process, called the Risorgimento. That process was influenced by the Savoy-led Kingdom of Sardinia, which was one of Italy's legal predecessor states. In 1882 it became a colonial empire, establishing the Italian Empire.

In 1866, Italy declared war on Austria in alliance with Prussia and, upon its victory, received the region of Veneto. Italian troops entered Rome in 1870, ending more than one thousand years of Papal temporal power. In the last two decades of the 19th century, Italy developed into a colonial power, and in 1882 it entered into a Triple Alliance with the German Empire and the Austro-Hungarian Empire, following strong disagreements with France about their respective colonial expansions. Although relations with Berlin became very friendly, the alliance with Vienna remained purely formal, due in part to Italy's desire to acquire Trentino and Trieste from Austria-Hungary. As a result, Italy accepted the British invitation to join the Allied Powers during World War I, as the western powers promised territorial compensation (at the expense of Austria-Hungary) for participation that was more generous than Vienna's offer in exchange for Italian neutrality. Victory in the war gave Italy a permanent seat in the Council of the League of Nations, but it did not receive all the territories it was promised.

The Central Powers, also known as the Central Empires, were one of the two main coalitions that fought in World War I (1914–1918). It consisted of the German Empire, Austria-Hungary, the Ottoman Empire, and the Kingdom of Bulgaria; this was also known as the Quadruple Alliance.

The Central Powers' origin was the alliance of Germany and Austria-Hungary in 1879. Despite having nominally joined the Triple Alliance before, Italy did not take part in World War I on the side of the Central Powers and later joined on the side of the Allies. The Ottoman Empire and Bulgaria did not join until after World War I had begun. The Central Powers faced, and were defeated by, the Allied Powers, which themselves had formed around the Triple Entente. They dissolved in 1918 after they lost the war.

The Allies or the Entente (UK: /ɒ̃ˈtɒ̃t/, US: /ɒnˈtɒnt/ on-TONT) was an international military coalition of countries led by the French Republic, the United Kingdom, the Russian Empire, the United States, the Kingdom of Italy, and the Empire of Japan against the Central Powers of the German Empire, Austria-Hungary, the Ottoman Empire, and the Kingdom of Bulgaria in World War I (1914–1918).

By the end of the first decade of the 20th century, the major European powers were divided between the Triple Entente and the Triple Alliance. The Triple Entente was made up of the United Kingdom, France, and Russia. The Triple Alliance was originally composed of Germany, Austria–Hungary, and Italy, but Italy remained neutral in 1914. As the war progressed, each coalition added new members. Japan joined the Entente in 1914 and, despite proclaiming its neutrality at the beginning of the war, Italy also joined the Entente in 1915. The term "Allies" became more widely used than "Entente", although the United Kingdom, France, Russia, and Italy were also referred to as the Quadruple Entente and, together with Japan, as the Quintuple Entente. The five British Dominions (Australia, Canada, New Zealand, Newfoundland, and the Union of South Africa) all fought alongside the British. The colonies of Allied countries, such as the American Philippines, Belgian Congo, British India, French Algeria, and Japanese Korea, were also used as a source of manpower by the colonial powers.

A military alliance is a formal agreement between nations that specifies mutual obligations regarding national security. In the event a nation is attacked, members of the alliance are often obligated to come to their defense regardless if attacked directly. Military alliances can be classified into defense pacts, non-aggression pacts, and ententes. Alliances may be covert (as was common from 1870 to 1916) or public.

According to a 2002 dataset of military alliances, there have been 538 alliance treaties from 1815 to 2003. The vast majority of the alliances involve commitments to come to the military support of one ally involved in war. The vast majority are defensive in nature. Since the end of the Second World War, military alliances have usually behaved less aggressively and act more as a deterrent. A 2025 analysis of alliances across the 19th and 20th century found that alliances overall tend to deter war.

Victor Emmanuel III (Italian: Vittorio Emanuele Ferdinando Maria Gennaro di Savoia; 11 November 1869 – 28 December 1947) was King of Italy from 29 July 1900 until his abdication on 9 May 1946. A member of the House of Savoy, he also reigned as Emperor of Ethiopia from 1936 to 1941 and King of the Albanians from 1939 to 1943, following the Italian invasions of Ethiopia and Albania. During his reign of nearly 46 years, which began after the assassination of his father Umberto I, the Kingdom of Italy became involved in two world wars. His reign also encompassed the birth, rise, and fall of the Fascist regime.

The first fourteen years of Victor Emmanuel's reign were dominated by prime minister Giovanni Giolitti, who focused on industrialization and passed several democratic reforms, such as the introduction of universal male suffrage. In foreign policy, Giolitti's Italy distanced itself from the fellow members of the Triple Alliance (the German Empire and Austria-Hungary) and colonized Libya following the Italo-Turkish War. Giolitti was succeeded by Antonio Salandra, Paolo Boselli, and Vittorio Emanuele Orlando. The First World War brought about Italian victory over the Habsburg Empire and the annexation of the Italian-speaking provinces of Trento and Trieste, completing the national unity of Italy, and the southern part of German-speaking Tyrol (South Tyrol). For this reason, Victor Emmanuel was labelled the "King of Victory". However, a part of Italian nationalists protested against the partial violation of the 1915 Treaty of London and what they defined as a "mutilated victory", demanding the annexation of Croatian-speaking territories in Dalmatia and temporarily occupying the town of Fiume without royal assent.

The Franco-Russian Alliance (French: Alliance Franco-Russe, Russian: Франко-Русский Альянс, romanized: Franko-Russkiy Al'yans), also known as the Dual Entente or Russo-French Rapprochement (Rapprochement Franco-Russe, Русско-Французское Сближение; Russko-Frantsuzskoye Sblizheniye), was an alliance formed by the agreements of 1891–94; it lasted until 1917. The strengthening of the German Empire, the creation of the Triple Alliance of 1882, and the exacerbation of Franco-German and Russo-German tensions at the end of the 1880s led to a common foreign policy and mutual strategic military interests between France and Russia. The development of financial ties between the two countries created the economic prerequisites for the Russo-French Alliance.

Although a member of the Triple Alliance, Italy did not join Germany and Austria-Hungary when the conflict started in 1914, on the ground that war was initiated by the two Central Powers while the Triple Alliance was a defensive bloc. 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 any compensation 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, after the Russian collapse allowed the Central Powers to move reinforcements to the Italian Front from the Eastern Front.