the neighboring states. Oyo led a successful campaign into Mahi territory north of Dahomey in the late 18th century. The Yoruba also used the forces of their tributaries; for instance, they accomplished a 1784 naval blockade of Badagri with an Oyo-Dahomey-Lagos force. Organization At the beginning, the people were concentrated in metropolitan Oyo. With imperial expansion, Oyo reorganized to better manage its vast holdings within and outside of Yorubaland. It was divided into four layers defined by relation to the core of the empire. These layers were Metropolitan Oyo, southern Yorubaland, the Egbado Corridor and Ajaland. Metropolitan Oyo Metropolitan Oyo corresponded, more or less, to the Oyo state prior to the Nupe invasion. This was the hub of the empire, where the Yoruba spoke the Oyo dialect. Metropolitan Oyo was divided into six provinces, with three on the west side of the Ogun River and three to the river's east. Each province was supervised by a governor appointed directly by the Alaafin of Oyo. Yorubaland The second layer of the empire was composed of the towns closest to Oyo-Ile, which were recognized as brothers. This area was south of metropolitan Oyo, and its Yoruba inhabitants spoke different dialects from that of Oyo. These tributary states were led by their own rulers, titled Obas, who were confirmed by the Alaafin of Oyo. Egbado Corridor The empire's third layer was the Egbado Corridor southwest of Yorubaland. This area was inhabited by the Egba and Egbado, and guaranteed Oyo's trade with the coast. The Egba and Egbado tributaries were allowed, like their Yoruba counterparts, to rule themselves. They were, however, supervised by Ajele. These were agents appointed by the Alaafin of Oyo to oversee his interest and monitor commerce. The lead representative of Oyo in the corridor was the Olu, ruler of the town of Ilaro. Ajaland Ajaland was the last layer added to the empire. It was the most restive and distant, and kept in line with threats of expeditions against it. This territory extended from the non-Yoruba areas west of the Egbado Corridor far into Ewe controlled territory in modern Togo. This area, like all tributary states, was allowed a fair degree of autonomy as long as taxes were paid, the orders from Oyo were strictly followed, and access to local markets was provided to Oyo merchants. The Oyo often demanded tribute in slaves. The tributary chiefs of other kingdoms sometimes