But, elated by his comparatively easy successes over the Spaniards, he proceeded to turn his attention toward the south, where the French had pushed their outposts into the fertile valley of the Ouergha, a region on which the Riffian leader depended for his supplies. Whether the French were responsible for precipitating the conflict which ensued by entering the Riff, or whether the Riffi first invaded territory under French protection, is open to some question. In any event, the spring of 1924 found the warriors of Abd-el-Krim formed in two lines of battle, one facing the Spaniards on the north, the other confronting the French on the south. For many months the tide of battle ran in favor of the Riffi, for the Spaniards were discouraged by disasters at the front and by political disorders at home; while the French, who had vastly underestimated the strength of their enemy, were slow in bringing up sufficient men and guns. [Illustration: FROM OUT OF THE UNKNOWN Strange masked mendicants drift into the Saharan border towns, their progress marked by the throb of desert drums] Although, by the summer of 1925, the French and Spaniards had in the field between them a force which probably exceeded half a million men, under forty generals, two marshals of France, Lyautey and Pétain, and the Spanish dictator, Primo de Rivera, the outcome of the campaign, which had all but bankrupted Spain and was said to be costing France a million dollars a day, was by no means certain. In fact, so eager was France for encouragement, if not for reinforcement, that she accepted the services of a group of young American aviators who during the Great War had served with distinction in the Lafayette Escadrille. As the laws of France do not permit the enlistment of foreigners in any branch of her army save the Foreign Legion, the difficulty was solved by forming the American volunteers into a unit known as the Shereefian Air Guard and having them take service under the sultan of Morocco, against whose authority, as nominal sovereign of the whole empire, the Riffi were technically in rebellion. That these young Americans, in their thirst for excitement and adventure, should have seen fit to take service under an African ruler is surprising enough, but that they should have bombed and raked with machine-gun fire the defenseless villages of a people with whom they had no quarrel, a people who were fighting for independence, is incomprehensible to those who had been the first to applaud their achievements in the air during the Great War. They claimed to be fighting for France, yet France, with one of the most powerful air forces in the world, did not need them. In effect, then, they were fighting to perpetuate the rule in the Riff of Spain, a country whom the preceding generation of Americans had driven from her last foothold in the New World because her tyranny and cruelty stank in the nostrils of decent men.