Nelson's history of the war. Vol. XI., The struggle for the Dvina, and the great invasion of Serbia

THE OVERRUNNING OF SERBIA. 129

miles adjoined unfriendly Bosnia ; then for a little came the protection of Montenegro ; but the southern part was bounded by Albania, which was at least potentially hostile. If the Serbian army were forced back in the north it could retire by the valleys of the Morava and the Vardar towards Salonika. By these valleys, which are followed by roads and railways, Serbia could receive supplies from the Allied base on the sea. If the only force was von Mackensen’s, she might well hope to stand on the ridges behind the northern plain, as she had stood nine months before, and hold the invader.

But with Bulgaria on her flank the situation was wholly changed. The Bulgarian right, moving against the Timok valley, must sooner or later join hands with von Mackensen, and force the Serbians south and west of the Constantinople railway. Such a position would be serious, but not desperate, for a stand might still be made on the hills of the Upper Morava, and communication kept open with Salonika. But in the south the Bulgarian frontier comes very close to the vital railway from the sea. Vrania is only twenty miles off. Strumnitza station is less, and the nodal point of Uskub is only fifty. It would be an easy task for the Bulgarian southern armies to cut the line. Once that happened there was no way of provisioning the Serbian forces except by the difficult hill paths of Albania and the Black Mountain. There was no way of retreat for them except into the wild recesses of the coastal mountains and the gorges of the Black and White Drin. Once such a retreat was compelled, Serbia would be overrun and the Serbian army put out of action.

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