General von Falkenhayn, co-operating with von Mackensen, smashed his way through Vulkan Pass, and cut the main line running to Bucharest at Craiova. The Dobrudja region was overrun and the central Roumanian plain was swept clear of all Roumanian opposition to the German advance. The seat of government was transferred from Bucharest to Jassy on November 28, 1916, and on December 6th Bucharest was entered by von Mackensen, definitely putting an end to Roumania as a factor in the war. The immediate result of the fall of Roumania was to release immense stores of petroleum for German use. British and Roumanian engineers had done their utmost by the use of explosives to make useless the great Roumanian oil wells, but German engineers soon had the precious fluid in full flow. This furnished the fuel which Germany had long and ardently desired. The oil-burning submarine now came into its own. It was possible to plan a great fleet of submersibles to attempt execution of von Tirpitz’s plan for unrestricted submarine warfare. This was decided upon by the German High Command the day Bucharest fell. It was realized that such a policy would bring the United States into the war, but the Kaiser and his advisers hoped the submarine on sea and a great western front offensive on land would force a decision in favor of Germany before America could get ready. How that hope failed was revealed at Château-Thierry and in the humiliation of Germany. CHAPTER VII CAMPAIGN IN MESOPOTAMIA In our previous discussion of the British campaign in Mesopotamia we left the British forces intrenched at Kurna, and also occupying Basra, the port of Bagdad. The object of the Mesopotamia Expedition was primarily to keep the enemy from the shores of the Gulf of Persia. If the English had been satisfied with that, the misfortune which was to come to them might never have occurred, but the whole expedition was essentially political rather than military in its nature. The British were defending India. The Germans, unable to attack the British Empire by sea, were hoping to attack her by land. They had already attempted to stir up a Holy War with the full expectation that it would lead to an Indian revolution. In this they had failed, for the millions of Mohammedans in India cared little for the Turkish Sultan or his proclamations. Through Bagdad, however, they hoped to strike a blow at the English influence on the Persian Gulf. The English, therefore, felt strongly that it was not enough to sit safely astride the Tigris, but that a blow at Bagdad would produce a tremendous political effect. It would practically prevent German communication with Persia, and the Indian frontier.