The war was primarily supported by nationalists, industrial producers, and imperialists.
In the Balkans, Yugoslav nationalists such as Yugoslav nationalist leader Ante Trumbić in the Balkans strongly supported the war, desiring the freedom of Yugoslavs from Austria-Hungary and other foreign powers and the creation of an independent Yugoslavia. The Yugoslav Committee was formed in Paris on 30 April 1915 but shortly moved its office to London, Trumbić led the Committee.
In the Middle East, Arab nationalism soared in Ottoman territories in response to the rise of Turkish nationalism during the war, with Arab nationalist leaders advocating the creation of a pan-Arab state. In 1916, the Arab Revolt began in Ottoman-controlled territories of the Middle East in an effort to achieve independence.
Italian nationalism was stirred by the outbreak of the war and was initially strongly supported by a variety of political factions. One of the most prominent and popular Italian nationalist supporters of the war wasGabriele d'Annunzio who promoted Italian irredentism and helped sway the Italian public to support intervention in the war. The Italian Liberal Party under the leadership of Paolo Boselli promoted intervention in the war on the side of the Allies and utilised the Dante Aligheri Society to promote Italian nationalism.
A number of socialist parties initially supported the war when it began in August 1914. Initially European socialists became split on national lines with the conception of class conflict held by radical socialists such as Marxists and syndicalists being overstepped by their support for war. Once the war began, Austrian, British, French, German and Russian socialists followed the rising nationalist current by supporting their country's intervention in the war.
Italian socialists were divided on whether to support the war or oppose it, some were militant supporters of the war including Benito Mussolini and Leonida Bissolati. However the Italian Socialist Party decided to oppose the war after anti-militarist protestors had been killed, resulting in a general strike called Red Week. The Italian Socialist Party purged itself of pro-war nationalist members, including Mussolini.Mussolini, a syndicalist who supported the war on grounds of irredentist claims on Italian-populated regions of Austria-Hungary, formed the pro-interventionist Il Popolo d'Italia and the Fasci Riviluzionario d'Azione Internazionalista ("Revolutionary Fasci for International Action") in October 1914 that later developed into the Fasci di Combattimento in 1919 and the origin of fascism. Mussolini's nationalism enabled him to raise funds from Ansaldo (an armaments firm) and other companies to create Il Popolo d'Italia to convince socialists and revolutionaries to support the war.
In April 1918 the Rome Congress of Oppressed Nationalities was held that included Czechoslovak, Italian, Polish, Transylvanian, and Yugoslav representatives that urged the Allies to support national self-determination for the peoples residing within Austria-Hungary.