<P> On the Trentino front, the Austro - Hungarians took advantage of the mountainous terrain, which favoured the defender . After an initial strategic retreat, the front remained largely unchanged, while Austrian Kaiserschützen and Standschützen engaged Italian Alpini in bitter hand - to - hand combat throughout the summer . The Austro - Hungarians counterattacked in the Altopiano of Asiago, towards Verona and Padua, in the spring of 1916 (Strafexpedition), but made little progress . </P> <P> Beginning in 1915, the Italians under Cadorna mounted eleven offensives on the Isonzo front along the Isonzo (Soča) River, northeast of Trieste . All eleven offensives were repelled by the Austro - Hungarians, who held the higher ground . In the summer of 1916, after the Battle of Doberdò, the Italians captured the town of Gorizia . After this minor victory, the front remained static for over a year, despite several Italian offensives, centred on the Banjšice and Karst Plateau east of Gorizia . </P> <P> The Central Powers launched a crushing offensive on 26 October 1917, spearheaded by the Germans . They achieved a victory at Caporetto (Kobarid). The Italian Army was routed and retreated more than 100 kilometres (62 mi) to reorganise, stabilising the front at the Piave River . Since the Italian Army had suffered heavy losses in the Battle of Caporetto, the Italian Government called to arms the so - called' 99 Boys (Ragazzi del' 99): that is, all males born 1899 and prior, and so were 18 years old or older . In 1918, the Austro - Hungarians failed to break through in a series of battles on the Piave and were finally decisively defeated in the Battle of Vittorio Veneto in October of that year . On 1 November, the Italian Navy destroyed much of the Austro - Hungarian fleet stationed in Pula, preventing it from being handed over to the new State of Slovenes, Croats and Serbs . On 3 November, the Italians invaded Trieste from the sea . On the same day, the Armistice of Villa Giusti was signed . By mid-November 1918, the Italian military occupied the entire former Austrian Littoral and had seized control of the portion of Dalmatia that had been guaranteed to Italy by the London Pact . By the end of hostilities in November 1918, Admiral Enrico Millo declared himself Italy's Governor of Dalmatia . Austria - Hungary surrendered on 11 November 1918 . </P> <P> Romania had been allied with the Central Powers since 1882 . When the war began, however, it declared its neutrality, arguing that because Austria - Hungary had itself declared war on Serbia, Romania was under no obligation to join the war . When the Entente Powers promised Romania Transylvania and Banat, large territories of eastern Hungary, in exchange for Romania's declaring war on the Central Powers, the Romanian government renounced its neutrality . On 27 August 1916, the Romanian Army launched an attack against Austria - Hungary, with limited Russian support . The Romanian offensive was initially successful, against the Austro - Hungarian troops in Transylvania, but a counterattack by the forces of the Central Powers drove them back . As a result of the Battle of Bucharest, the Central Powers occupied Bucharest on 6 December 1916 . Fighting in Moldova continued in 1917, resulting in a costly stalemate for the Central Powers . Russian withdrawal from the war in late 1917 as a result of the October Revolution meant that Romania was forced to sign an armistice with the Central Powers on 9 December 1917 . </P>

Which of the following events is regarded as starting world war i