Even with the decision to retreat taken, the Franco-British forces were not "out of the wood." The withdrawal had to be made down a single-track railway, through a country without roads—converted by the autumn rains into a swamp—and in face of a pursuing enemy. The retreat was made by echelons, in four stages, and only by a narrow margin did the French frustrate Bulgarian efforts to outflank and cut their retreat, first at the Demir Qapu defile, and again at Strumitsa station. The British, too, on the right were heavily attacked, and any weakening of their line at this critical juncture might have been fatal to the extrication of the Allied forces from the noose into which they had been pushed.
Fortunately, once the Greek frontier was regained the pursuit halted—mainly because the Germans were reluctant to undertake further commitments in the Balkans to the detriment of their strength in other theatres. Falkenhayn held that the Macedonian operations should be left to the Bulgarians, but this policy over looked the fact that the Greeks, however friendly to the Germans, would have resented any invasion of their territory by the Bul garians. Thus by Dec. 12 the retreating forces were safely out of reach of their pursuers, facing them across the frontier. After pausing for a few days on a line stretching roughly from Soro viCevo to Lake Doiran, the withdrawal was resumed, and by Dec. 18 the forces of Sarrail and Mahon were back in the vicinity of Salonika. Covering this base an entrenched line was constructed, on an 8om. arc stretching from the mouth of the Vardar through Doganji to the Gulf of Orfano, and occupied early in the new year.
1916 were the Bulgarian I. and II. Armies and the German XI. Army—a total of some 280,000 men—aligned on a front from Lake Okhrida on the west to the point where the Struma enters Bulgaria on the east. But from March onwards the drain on the German forces at Verdun led Falkenhayn to withdraw the Ger man troops, all but one division; by 1918 the XI. Army, though. German in name and in staff, contained only one complete Ger man battalion.
On the Entente side the reaction of Verdun took the form of orders from Joffre to Sarrail to pin down the enemy on his front, in order if possible to prevent Falkenhayn drawing upon the forces there. Accordingly the French moved out west of the Vardar towards Vodena and the British advanced north to Kukus. This advance, although it lengthened the front to be defended and the lines of communication, was of essential value for the se curity of the Allied force, for the entrenched position at Salonika itself was dominated from the mountains east of the town, and might become untenable if these heights were occupied by the enemy. But in how small degree the Allied advance fixed the Ger mans can be gauged from the previous paragraph, and Sarrail, who had been placed under Joffre's supreme command in Dec., received instructions not only to operate with greatly increased vigor on the Salonika front but also to prepare and organize a definite offensive to be launched simultaneously with the antici pated entry of Rumania into the war.
Meantime the situation was complicated by a Greek incident; until 1918 politics were to play a larger part in the Salonika the atre than war. The neutral Greek forces, five corps, were distributed throughout the region, in theory to guard the fron tier; and such a situation, while Gilbertian in its absurdity to the distant observer, was a source of serious anxiety to the Franco British forces on the spot. Feeling that they would be safer without such dubious protection, they brought diplomatic pres sure to bear on the Greek Government for the withdrawal of the Greek forces from Macedonia and their demobilization. Reluc tantly the Greeks complied, but while the Allies occupied certain of their forts the Bulgarians seized the opportunity to cross the frontier, and appeared before Fort Rupel, which commanded the Struma gate into the Macedonian plain. The Greek commander thereupon handed over the fort to them (May 26).