As far as Aleppo, troops and supplies from Europe passed over one common route. From the Turkish point of view, therefore, the campaigns in these two countries were to some extent interdependent. This enabled the Turks to concentrate a reserve at Aleppo, ready to be moved down into either theatre of war as the exigencies of the situation might demand. Conversely, therefore, a British offensive in Mesopotamia might draw off troops destined for Palestine, or an offensive in Palestine might attract troops otherwise intended for operations in Mesopotamia. There is strong evidence that a Turco-German offensive was contemplated in Mesopotamia for 1918. In the spring of that year, however, a British offensive was undertaken in Palestine, which had the immediate effect of drawing to that country strong Turkish and German reinforcements from Aleppo. Nothing more was heard of the offensive in Mesopotamia, and, by the autumn of 1918, there was scarcely a fighting Turk to be found in that country. Just as our expedition against the Dardanelles, by engaging the enemy at a vital spot near home, had materially assisted the defence of Egypt, so did our offensives in Palestine materially assist the defence of Mesopotamia.

Turning to another corner of the map of Turkey, where Europe and Asia meet in the mountains of the Caucasus, we see that the Turkish frontier here marches with that of Russia. In the earlier days of the war, the Russians carried out an important and successful advance in this neighbourhood, and, early in 1916, occupied the cities of Trebizond and Erzerum. Thus, at the time when the campaign in Palestine was embarked upon, the armies of the allies were closing in upon Eastern Turkey simultaneously from three directions, the Russian Caucasus army from the north-east, the British Mesopotamian army from the south-east, and the Egyptian Expeditionary Force from the south. Strategically, the situation seemed full of promise. But, in the winter of 1917-18, followed the disastrous collapse of Russia, and the setting free of many Turkish soldiers of good quality from all the Russian fronts for service elsewhere. We had hoped that our offensive in Syria might have been supported by the co-operation of the Russians. Instead, we felt the pinch of their defection in the stiffening of enemy resistance on our front by the transfer of good troops from the Caucasus to Palestine.

There is yet another theatre of warfare in Asiatic Turkey, the operations in which exerted considerable influence on those in Palestine. The whole of the eastern shores of the Red Sea formed part of the Ottoman Empire. The southernmost sector, known as the Yemen, was the farthest outpost of that Empire. Here a few Turks and Arabs conducted a sporadic warfare against our garrison at Aden, more calculated to cause annoyance and to detain a British force of some strength than to exercise much influence upon the war as a whole.

Farther to the north, on this Red Sea littoral, is a province of much more importance, the Hejaz, in which are situate the most holy of cities in the Moslem world, Mecca and Medina. To Christians, the Hejaz is forbidden ground. To Mahomedans, it is the focus of pilgrimage from all parts of the world. The Sultan of Turkey, as the ruler of Mecca, is looked up to by the Sunni or orthodox Mahomedans in all lands as the spiritual head of their Church. Though rulers of the Hejaz, the Turks were not at one with the local population. These are Arabs, and to them the Turkish rule was as unpopular as to most other non-Turkish subjects of that decaying Empire. Profiting by Turkey's embarrassments in other parts, the Arabs rose in the summer of 1916, resolved on ridding themselves of the hated Turkish yoke. Sheikh Hussein of Mecca was proclaimed King of the Hejaz.

At this time there were garrisons of Turkish troops stationed at Mecca, Medina and at the port of Jiddah. Their communication with Turkey was by the recently opened railway to Damascus and Aleppo. This railway, south of Damascus, ran along the high plateau on the eastern side of the Dead Sea, through Maan, and along the desert to Medina. The intention was to carry the line ultimately through to Mecca, but at this time it was only open for traffic as far as Medina. The revolt broke out on the 5th June, 1916, at which date a cordon was spread round Medina. Jiddah was attacked on the 9th, and capitulated after holding out for only a week. The bulk of the Mecca garrison were at this time at Taif. Accordingly, the town of Mecca passed into the hands of the Emir, with the exception of the ports. These put up a small fight, but had all surrendered by the middle of July. The force at Taif were blockaded, and, on the 23rd September, this force also surrendered. By this time, all the outlying garrisons had been disposed of, and the Hejaz generally cleared of Turks.

Meanwhile, Medina had not only held out, but had been reinforced, and the fighting strength brought up to some 14,000. Late in September, the Turks sallied out and established a cordon of posts at a distance of some 30 to 40 miles from the city. They also pushed further afield; but, Arab armies moving up from the south, the Turks withdrew, at the end of the year, behind the cordon of posts which they had established. For the next six months, the railway to the north of Medina was frequently raided by the Arabs, but the town was effectually cut off from its communications with Turkey.

In July, 1917, Akaba, at the head of the gulf of that name, the north-eastern arm of the Red Sea, was captured. This is at no great distance from Maan, an important depot on the Hejaz Railway, the last outpost of Syria at the edge of the desert of North Arabia. From Akaba, the railway was now attacked at Maan, with serious results to Medina; nevertheless, that city continued to hold out, and was probably never very closely invested.

In October and November, 1917, about the time of the third battle of Gaza, the Turks were still in Maan, and tried to assume the offensive against the Arabs, but proved too weak to succeed. After the fall of Jerusalem, the Turks withdrew to some extent, and the Arabs advanced towards the lands east of the Dead Sea.

From this period forward, the history of the Hejaz revolt merges in that of the Palestine campaign. The Arab forces east of the Dead Sea afforded a safeguard against any possible Turkish attempt to move round our right flank and raid our line of communications. In February and in March, 1918, Turkish expeditions moving against the Arab forces of the King of the Hejaz southward from Kerak, near the south-eastern corner of the Dead Sea, met with failure. The former expedition ended in disaster, and the latter was forced to withdraw, owing to the imminence of a British crossing of the Jordan in its rear. Arab activity on the railway now definitely isolated Medina. Although the Arabs were never strong enough to push a powerful force up through Eastern Palestine, yet the presence of a friendly force operating in that country exercised considerable influence upon the later stages of the Palestine campaign. The assistance which the Arabs gave in the ultimate destruction of the Turkish army was invaluable.