Austria had proved capable of holding the Italians on the Isonzo, and once the Russian danger began to fade under the pressure of the summer offensive, her command was anxious to deal with Serbia conclusively. Austria's attempted invasions in August and September 1914, and again in November, had been brusquely repulsed by Serbian counter-strokes, and it was not pleasant for a great Power, especially one with so many Slav subjects, to swallow such military rebuffs. Her impatience coin cided with Falkenhayn's desire to gain direct railway communica tion with Turkey, hard pressed at the Dardanelles. Throughout the summer the rival coalitions had been bidding for Bulgaria's support, and in this bargaining the Entente suffered the moral handicap of military failure and the material handicap caused by Serbia's unwillingness to give up any part of Macedonia—of which she had despoiled Bulgaria in 1913. As Austria had no ob jection to offering territory that belonged to her enemy, Bulgaria accepted her bid. This accession of strength enhanced the chance of a decision against Serbia and in August Falkenhayn decided to reinforce Kiivess's Austrian 3rd Army with Gallwitz's German 11th Army from the Russian front. In addition two Bulgarian armies were available. Mackensen was sent to direct the opera tions. To meet this new threat Serbia, apart from her own rela tively small forces, had only a treaty guarantee of Greek aid and promises from the Entente Powers. The first disappeared with the fall of Venizelos, the pro-Ally Greek premier, and the second, as usual, was too late.
On Oct. 6, 1915 (see further, SERBIAN CAMPAIGNS) the Austro German armies attacked southwards across the Danube, with a flanking movement across the Drina on the right. The sturdy resistance of the Serbs in delaying actions, and the natural diffi culty of the mountainous country, checked the advance, but be fore Franco-British reinforcements could arrive, the Bulgarian armies struck westwards into southern Serbia, across the rear of the main Serbian armies. This drove a deep wedge between the Serbs and their allies, moving up from Salonika, and automati cally loosened the props of the resistance in the north. With their line bent at both ends until it resembled a vast bow, threatened with a double envelopment, and with their retreat to the south cut off, the Serbian armies decided to retire west through the Albanian mountains. Those who survived the hardships of this mid-winter retreat were conveyed to the island of Corfu, and after being re-equipped and reorganized, joined the Entente force at Salonika in the spring of 1916. The conquest of Serbia, though not, as it proved, of Serbian military power, relieved Austria of danger on her southern frontier, and gave Germany free com munication and control over a huge central belt from the North sea to the Tigris. For the Entente this campaign dug a military sump-pit which for three years was to drain their military re sources, there to lie idle and ineffective. Yet ultimately that sump pit was to overflow and wash away one of the props of the Central Alliance.
force—which was under the command of Gen. Sarrail—pressed up the Vardar and over the Serbian frontier, only to find that the Bulgarian wedge had cut it off from the Serbians, and it was forced to fall back on Salonika, pursued by the Bulgarians. On military grounds an evacuation of Salonika was indicated, but political reasons induced the Allies to remain. The Dardanelles failure had already diminished their prestige, and by convincing the Balkan States of German invincibility had induced Bulgaria to enter the war and Greece to break her treaty with Serbia. To evacuate Salonika would be a further loss of prestige, whereas by holding on the Allies could check German influence over Greece, and maintain a base of operations from which to aid Rumania, if, as expected, she entered the war on their side. To this end the Salonika force was augmented with fresh British and French divi sions, as well as contingents from Italy and Russia, and there also the rebuilt Serbian army was brought. But apart from the cap ture of Monastir in Nov. 1916, and an abortive attack in April 1917, the Entente force made no serious offensive until the au tumn of 1918. Its innocuousness was partly due to the natural difficulties of the country—the chain of mountain ridges which guarded the approach to the Balkans, partly to the feeling of the Allied Governments that it was a bad debt, and partly to the personality of Sarrail, whose conduct and reputation for political intrigues failed to command the confidence and co-operation es sential if such a mixed force was to "pull its weight." On their side the Germans were content to leave it in passivity, under guard of the Bulgarians, while they steadily withdrew their own forces for use elsewhere. With gentle sarcasm they termed Salon ika their "largest internment camp," and with half a million Allied troops locked up there the jibe had some justification—until 1918. (See further SALONIKA CAMPAIGN.) The Mesopotamia Expedition to the Fall of Kut.—Nor was Salonika the only "drain" opened in 1915. Mesopotamia was the site of a fresh diversion of force from the centre of military gravity, and one which could only be excused on purely political grounds. It was not, like Salonika and the Dardanelles, begun to relieve a hard-pressed ally, nor had it the justification of the Dardanelles expedition of being directed at the vital point of one of the enemy States. The occupation of Mesopotamia might raise British prestige, and it might annoy Turkey, but it could not endanger her power of resistance. Although its origin was sound, its development was another example of "drift," due to the inherent faultiness of Britain's machinery for the conduct of war. (See further MESOPOTAMIA, OPERATIONS IN.) The oilfields near the Persian gulf were of essential importance for Britain's oil supply, and thus when war with Turkey was imminent, a small Indian force, of one division, was despatched to safeguard them. To fulfil this mission effectively it was neces sary to occupy the Basra vilayet at the head of the Persian gulf, in order to command the possible lines of approach.