These capital mistakes made by the Allies are as follows. They believed that a friendly agreement with Bulgaria was possible, although that country was treaty-bound to Berlin and Constantinople long before the war. They cherished illusions concerning King Constantine, who, above all else, was brother-in-law of the Kaiser. They organized the Dardanelles expedition, which should never have been attempted. Even if this operation had been judged technically feasible, its futility would have been apparent if the Allies had realized—and it was their arch-error not to realize—that the strategic key to the whole European war was the Danube. The mere occupation by the Allies of the territory stretching from Montenegro through Serbia to Roumania, would have resolved all the essential problems of the conflict. Cut off from the Central Empires, Bulgaria and Turkey, whose arsenals were depleted by the Balkan disturbances of 1912-1913, would have found it impossible to make a strong stand against the Allies. Turkey, who had been imprudent enough to defy them, would have been obliged to open the Straits within a very short time, for sheer lack of munitions to defend them. This opening of the Straits would have been effected by a strong pressure by the Allies on the south of Hungary. Moreover, by the same action the Central Empires would have been barred from reinforcements and supplies from the Orient. Germany, finding herself cut off on land in the South as she was blockaded by sea in the North, would have been obliged to come to terms. Unhappily, the general staffs of the Allies in the West were not prepared to grasp the politico-scientific character of the war, especially the cardinal importance of the economic factor. This ignorance remained unenlightened until Roumania was crushed in 1916. As a result, for twenty-seven months the Balkans were looked on by the leaders in the West as being of only secondary military importance. During these twenty-seven months the Allies were obsessed by the idea that they would vanquish Germany on the Western front by a war of attrition. This conviction delayed the Saloniki-Belgrade expedition, and when it was finally undertaken, it was on too small a scale to insure success. Such a grave error would never have been committed by the Allied strategists if they had fully realized that the principal objective of the Pan-German scheme, for the attainment of which Germany was primarily fighting, was the seizure of the Orient. This point of view, however, was for a long time ignored, in spite of the tireless efforts made by a few to demonstrate its vital importance.