Balkans theatre

A major cause of the war was the hostility between Serbia and Austria-Hungary, which made some of the earliest fighting take place between them. Serbia held out against Austria-Hungary for more than a year before it was conquered in late 1915.

Dalmatia was a strategic region during the war that both Italy and Serbia intended to seize from Austria-Hungary. Italy entered the war upon agreeing to the Treaty of London, 1915, which guaranteed Italy a substantial portion of Dalmatia.

In 1917, Greece entered the war for the Allieds, and in 1918, the multinational Allied Army of the Orient, based in northern Greece, finally launched an offensive, which drove Bulgaria to seek peace, recaptured Serbia and halted only at the border of Hungary in November 1918.

The Serbian army managed to rebuff the larger Austro-Hungarian Army because Russia assisted by invading from the north. In 1915, Austro-Hungary placed additional soldiers in the south front and succeed in engaging Bulgaria as an ally.

Soon, the Serbian army was attacked from the north and the east, forcing a retreat to Greece. Despite the loss, the retreat was successful, and the Serbian army remained operational in Greece with a newly-established base.

Italian soldiers in Vlorë, Albania during World War I. The tricolour flag of Italy, bearing the Savoy royal shield, is shown hanging alongside an Albanian flag from the balcony of the Italian prefecture headquarters.

Prior to direct intervention in the war, Italy had occupied the port of Vlorë in Albania in December 1914.[14] Upon entering the war, Italy spread its occupation to region of southern Albania beginning in autumn 1916.[14] Italian forces in 1916 recruited Albanian irregulars to serve alongside them.[14] Italy, with permission of the Allied command, occupied Northern Epirus on 23 August 1916, forcing the neutralist Greek army to withdraw its occupation forces there.[14]

In June 1917, Italy proclaimed central and southern Albania to be a protectorate of Italy. Northern Albania was allocated to the states of Serbia and Montenegro.[14] By 31 October 1918, French and Italian forces had expelled the Austro-Hungarian army from Albania.[14]

Dalmatia was a strategic region during World War I that both Italy and Serbia intended to seize from Austria-Hungary. Italy joined the Triple Entente Allies in 1915 upon agreeing to the London Pact, which guaranteed Italy the right to annex a large portion of Dalmatia in exchange for Italy's participation on the Allied side. From 5 to 6 November 1918, Italian forces were reported to have reached Lissa, Lagosta, Sebenico, and other localities on the Dalmatian coast.[15]

By the end of hostilities in November 1918, the Italian military had seized control of the entire portion of Dalmatia that had been guaranteed to Italy by the London Pact and, by 17 November, had seized Fiume as well.[16] In 1918, Admiral Enrico Millo declared himself Italy's Governor of Dalmatia.[16] The famous nationalist Gabriele d'Annunzio supported the seizure of Dalmatia and proceeded to Zadar in an Italian warship in December 1918.[17]

Bulgaria during World War I.

In the aftermath of the Balkan Wars Bulgarian opinion turned against Russia and the western powers, whom the Bulgarians felt had done nothing to help them. The government aligned Bulgaria with Germany and Austria-Hungary, even though this meant also becoming an ally of the Ottomans, Bulgaria's traditional enemy. But Bulgaria now had no claims against the Ottomans, whereas Serbia, Greece and Romania (allies of Britain and France) were all in possession of lands heavily populated by Bulgarians and thus perceived as Bulgarian.

Bulgaria, recuperating from the Balkan Wars, sat out the first year of World War I. When Germany promised to restore the boundaries of the Treaty of San Stefano, Bulgaria, which had the largest army in the Balkans, declared war on Serbia in October 1915. Britain, France and Italy then declared war on Bulgaria.

Although Bulgaria, in alliance with Germany and Austria-Hungary, won military victories against Serbia and Romania, occupying much of Southern Serbia (taking Nish, Serbia's war capital in November 5), advancing into Greek Macedonia, and taking Dobruja from the Romanians in September 1916, the war soon became unpopular with the majority of Bulgarian people, who suffered enormous economic hardship. The Russian Revolution of February 1917 had a significant effect in Bulgaria, spreading antiwar and anti-monarchist sentiment among the troops and in the cities.

In September 1918 the Serbs, British, French, Italians and Greeks broke through on the Macedonian front in the Vardar Offensive. While Bulgarian forces stopped them in Dojran and they didn't proceed to occupy Bulgarian lands, Tsar Ferdinand was forced to sue for peace.

In order to head off the revolutionaries, Ferdinand abdicated in favour of his son Boris III. The revolutionaries were suppressed and the army disbanded. Under the Treaty of Neuilly (November 1919), Bulgaria lost its Aegean coastline in favour of the Principal Allied and Associated Powers (transferred later by them to Greece) and nearly all of its Macedonian territory to the new state of Yugoslavia, and had to give Dobruja back to the Romanians (see also Dobruja, Western Outlands, Western Thrace).

In 1915, the Austro-Hungarians gained military support from Germany and, with diplomacy, brought in Bulgaria as an ally. Serbian forces were attacked from both north and south and were forced to retreat through Montenegro and Albania, with only 155,000 Serbs, mostly soldiers, reaching the coast of the Adriatic Sea and evacuated to Greece by Allied ships.

The Macedonian front stabilized roughly around the Greek border after the intervention of a Franco-British-Italian force that had landed in Salonica. The German generals had not let the Bulgarian army advance towards Salonika, because they hoped they could persuade the Greeks to join the Central Powers.

In 1918, after a prolonged build-up, the Allies, under the energetic French General Franchet d'Esperey, who led a combined French, Serbian, Greek and British army, attacked out of Greece. His initial victories convinced the Bulgarian government to sue for peace. He then attacked north and defeated the German and Austro-Hungarian forces that tried to halt his offensive.

By October 1918, his army had recaptured all of Serbia and was preparing to invade Hungary proper, but the offensive was halted by the Hungarian leadership offering to surrender in November 1918.

The French and British each kept six divisions on the Greek frontier from 1916 to the end of 1918. Originally, the French and British went to Greece to help Serbia, but with Serbia's conquest in the fall of 1915, their continued presence did not produce major effects and so they mobilized the useful forces to the Western Front. For nearly three years, those divisions accomplished essentially nothing and tied down only half of the Bulgarian army, which would not have gone far from Bulgaria anyway.

In mid 1918, led by General Franchet d'Esperey, those forces were added to conduct a major offensive on the south flank of the Quadruplice (8 French division, 6 British division, 1 Italian division, 12 Serbian division[18]). After the successul offensive launched on the 10th September 1918, they freed Belgrade and forced Bulgaria to Armistice on 29th September. That had a significative effect by threatening Austria-Hungary (which agreed to an rmistice on 4 November 1918) and then the German political leadership.

In fact, Keegan argued that "the installation of a violently nationalist and anti-Turkish government in Athens, led to Greek mobilization in the cause of the "Great Idea" - the recovery of the Greek empire in the east - which would complicate the Allied effort to resettle the peace of Europe for years after the war ended."[19]