coincided with more or less pronounced wet and dry periods. Several clans with traditions similar to those of the Donzas of the Borkou region, south of the Tibesti, settled in the range in the 16th and 17th centuries. These include the Keressa and Odobaya in the west, Foctoa in the northwest and northeast, and Emmeouia in the north. Several other clans—the Mogode in the west, Terintere in the north, Tozoba in the center, and Tegua and Mada in the south—are originally clans of the Bideyat people who immigrated from the Ennedi Plateau, southeast of Tibesti, around the same time. The Mada, however, have since largely emigrated to Borkou, Kaouar and Kanem. The early 17th century also saw the arrival of three clans from the region of Kufra to the northeast. The Taïzera settled in the plateau in the center and west of the mass, probably fleeing the Arab push into present-day Libya. According to oral tradition, their leader was initially rejected by the Daza clans and lived in isolation until winning the favor of a Dirsina woman. The Mahadena occupy the northeast quarter of the range and are likely from the Jalo oasis of Cyrenaica and thus related to the Mogharba Arab tribes, although an alternative hypothesis is that they are of Bideyat origin. Following years of conflict, a branch of the Mahadena clan, the Fortena, withdrew to the western margin of the Tibesti. The Fortena Mado ("Red Fortena") settled there, while the Fortena Yasko ("Black Fortena") pushed further west to Kaouar. The Tuareg people intermixed with the Toubou clans, especially with the early Goga clan, which produced the Gouboda, and with the later Arna clan, which produced the Mormorea. In both instances, the new clans were placed under the authority of suzerain clans of the traditionally feudal Tuareg, although they were eventually assimilated into the Toubou majority. Regional relations and colonization In the mid-19th century the Ottoman Empire began a campaign of territorial conquest across northern Africa from its regional headquarters in Libya, yet was unable to subdue the Tibesti. In 1890, to the chagrin of the Turks, France and Great Britain signed a declaration recognizing a French zone of influence in northern Africa from the Mediterranean Sea down to Lake Chad. In response, the Toubou allied with the Senussi Arabs of Libya and agreed that the southern half of the Tibesti could serve as a fallback base for