At the close of 1915 the main British force in Egypt was concerned with the defence of the Suez Canal against a threatened attack by the Turks from their Syrian bases. The Canal, as Moltke had long before told his countrymen, was for Britain a vital artery, and Egypt was the key of all her activities in the Near and Middle East. Suddenly, as is the fashion in the Orient, a new trouble blew up like a sandstorm in the desert. The Western frontier, some 700 miles long, adjoined the Italian possessions in Tripoli; but, though the Treaty of Lausanne had given Italy the suzerainty of that province, her writ ran feebly in the interior and her occupation had never been effective beyond the coast-line. When she declared war on Austria, she was compelled to leave the inland tribes to their own devices, and, stirred up by German and Turkish agents, they prepared for mischief. The chief of the Turkish agents was Nuri Bey, a half-brother of Enver, and about April 1915 a certain Gaafer arrived from Constantinople with large supplies of money and arms. His instructions were to mobilize the Arab and Berber tribes of the Libyan plateau for a dash upon Egypt from the west. The hope of the Turks in that region lay in the support of the great Senussi brotherhood. The Senussi form one of those strange religious fraternities familiar to the student of Northern Africa. Their founder had been a friend of Britain and had refused to cast in his lot with the Mahdi. He had preached a spiritual creed which orthodox Islam repudiated, and his followers had stood outside the main currents of Moslem life, holding apart from all secular politics, and declining any share in the propaganda of Pan-Islamism. Their headquarters were the oases of the Northern Libyan desert, and they looked without disfavour upon the rule of Britain in Egypt. Their Grand Sheikh, Sidi Ahmed, had at the outbreak of the war given assurance of friendliness to the Anglo-Egyptian authorities, and his official representatives dwelt on the banks of the Nile in good relations with the Government of Cairo. [Illustration: OPERATIONS ON THE WESTERN FRONTIER OF EGYPT.]