He even menaced Cordova, and compelled Ibn-Djahwar and his colleagues to enlist Berber mercenaries for its defence. He projected an expedition against the Christians, which failed on account of the treachery of the Emir of Badajoz, who repaid the previous misfortune to his arms with an ambuscade, which inflicted serious injury on the forces of Abul-Kasim and caused his retreat. Meanwhile, the isolated states and communities of the ancient khalifate were threatened with the recurrence of a deplorable political and social calamity. The depopulated provinces of Southern Spain, the incessant prevalence of hostility, the desire of sharing in the spoils of a country where their race had obtained incalculable wealth and absolute power, the insatiable thirst of military adventure, had produced, since the exaltation of the House of Ali, an enormous African immigration. The Berbers now swarmed in countless numbers over the plains to the south and west of the Sierra Morena, a region once considered the garden of Andalusia, and where their flocks still found a rich and abundant pasturage. Heretofore the allegiance of these unruly adventurers had been divided among a hundred petty chieftains, apparently incapable of harmony and united in nothing save an undying hatred of the indigenous population. Now, however, the case was altered. A national sentiment had arisen, which was soon confirmed by the inspiration of numbers, by the consciousness of strength, by the remembrance of injury, and by the hope of revenge. All eyes were turned towards Yahya, the ruler of Malaga, who, a Berber by descent and traditions, was also the representative of an African dynasty, and, for that reason, admirably qualified to be the leader of a national movement. The universal enthusiasm was artfully encouraged by the secret emissaries of the prince. The chieftains, with singular accord, surrendered their precarious authority. The passions of the barbarians were inflamed with the prospect of booty, and Yahya was publicly recognized as the head of the entire Berber party.