Support and opposition to the war

Support

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 was Gabriele 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.

Opposition

Rubble covered Sackville Street in Dublin after violence between Irish rebels and UK armed forces during the Easter Rising of 1916.

1917 – Execution at Verdun at the time of the mutinies.

The trade union and socialist movements had long voiced their opposition to a war, which they argued, meant only that workers would kill other workers in the interest of capitalism. Once war was declared, however, many socialists and trade unions backed their governments. Among the exceptions were the Bolsheviks, the Socialist Party of America, and the Italian Socialist Party, and individuals such as Karl Liebknecht, Rosa Luxemburg and their followers in Germany. There were also small anti-war groups in Britain and France.
Many countries jailed those who spoke out against the conflict. These included Eugene Debs in the United States and Bertrand Russell in Britain. In the U.S., the Espionage Act of 1917 effectively made free speech illegal and many served long prison sentences for statements of fact deemed unpatriotic. The Sedition Act of 1918 made any statements deemed "disloyal" a federal crime. Publications at all critical of the government were removed from circulation by postal censors.
A number of nationalists opposed intervention, particularly within states that the nationalists held hostility to. Irish nationalists staunchly opposed taking part in intervention with the United Kingdom of Great Britain and Ireland. The war had begun amid the Home Rule crisis in Ireland that had begun in 1912 and by 1914 there was a serious possibility of an outbreak of civil war in Ireland between Irish unionists and republicans. Irish nationalists and Marxists attempted to pursue Irish independence, culminating in the Easter Rising of 1916, with Germany sending 20,000 rifles to Ireland in order to stir unrest in the United Kingdom. The UK government placed Ireland under martial law in response to the Easter Rising.
Other opposition came from conscientious objectors – some socialist, some religious – who refused to fight. In Britain 16,000 people asked for conscientious objector status. Many suffered years of prison, including solitary confinement and bread and water diets. Even after the war, in Britain many job advertisements were marked "No conscientious objectors need apply".
The Central Asian Revolt started in the summer of 1916, when the Russian Empire government ended its exemption of Muslims from military service.
In 1917, a series of mutinies in the French army led to dozens of soldiers being executed and many more imprisoned.
In Milan in May 1917, Bolshevik revolutionaries organised and engaged in rioting calling for an end to the war, and managed to close down factories and stop public transportation. The Italian army was forced to enter Milan with tanks and machine guns to face Bolsheviks and anarchists who fought violently until May 23 when the army gained control of the city with almost fifty people killed (three of which were Italian soldiers) and over 800 people arrested.
The Conscription Crisis of 1917 in Canada erupted when conservative Prime Minister Robert Borden brought in compulsory military service over the objection of French-speaking Quebecers. Out of approximately 625,000 Canadians who served, about 60,000 were killed and another 173,000 were wounded.
In 1917, Emperor Charles I of Austria secretly entered into peace negotiations with the Allied powers, with his brother-in-law Sixtus as intermediary, without the knowledge of his ally Germany. He failed, however, because of the resistance of Italy.
In September 1917, the Russian soldiers in France began questioning why they were fighting for the French at all and mutinied. In Russia, opposition to the war led to soldiers also establishing their own revolutionary committees and helped foment the October Revolution of 1917, with the call going up for "bread, land, and peace". The Bolsheviks reached a peace treaty with Germany, the peace of Brest-Litovsk, despite its harsh conditions.
The end of October 1918, in northern Germany, saw the beginning of the German Revolution of 1918–19. Units of the German Navy refused to set sail for a last, large-scale operation in a war which they saw as good as lost, initiating the uprising. The sailors' revolt which then ensued in the naval ports of Wilhelmshaven and Kiel spread across the whole country within days and led to the proclamation of a republic on 9 November 1918 and shortly thereafter to the abdication of Kaiser Wilhelm II.

Conscription

As the war slowly turned into a war of attrition, conscription was implemented in some countries. This issue was particularly explosive in Canada and Australia. In the former it opened a political gap between French-Canadians, who claimed their true loyalty was to Canada and not the British Empire, and the Anglophone majority who saw the war as a duty to both Britain and Canada. Prime Minister Robert Borden pushed through a Military Service Act, provoking the Conscription Crisis of 1917. In Australia, a sustained pro-conscription campaign by Prime Minister Billy Hughes, caused a split in the Australian Labor Party and Hughes formed the Nationalist Party of Australia in 1917 to pursue the matter. Nevertheless, the labour movement, the Catholic Church, and Irish nationalist expatriates successfully opposed Hughes' push, which was rejected in two plebiscites.
Conscription put into uniform nearly every physically fit man in Britain, six of ten million eligible. Of these, about 750,000 lost their lives and 1,700,000 were wounded. Most deaths were to young unmarried men; however, 160,000 wives lost husbands and 300,000 children lost fathers.