height, spreading over twenty-five square kilometres, enclosed by three concentric rings of earthworks. By the late 15th century Benin was in contact with Portugal. At its apogee in the 16th and 17th centuries, Benin encompassed parts of southeastern Yorubaland and the western Igbo. In the Ethiopian Highlands, the Solomonic dynasty established itself in the 13th century. Claiming direct descent from the old Axumite royal house, the Solomonic ruled the region well into modern history. In the 16th century, Shewa and the rest of Abyssinia were conquered by the forces of Ahmed Gurey of the Adal Sultanate to the northwest. The conquest of the area by the Oromo ended in the contraction of both Adal and Abyssinia, changing regional dynamics for centuries to come. The Ajuran Empire, which was one of the largest and strongest empires in the Horn of Africa, began to decline in the 17th century, and several powerful successor states came to prominence. The Geledi Sultanate, established by Ibrahim Adeer, was a notable successor of the Ajuran Sultanate. The Sultanate reached its apex under the successive reigns of Sultan Yusuf Mahamud Ibrahim (reigned 1798 to 1848), who successfully consolidated Geledi power during the Bardera wars, and Sultan Ahmed Yusuf, who forced regional powers such as the Omani Empire to pay tribute. The Majeerteen Sultanate was a Somali Sultanate in the Horn of Africa. Ruled by King Osman Mahamuud during its golden age, it controlled much of northern and central Somalia in the 19th and early 20th centuries. The polity had all of the organs of an integrated modern state and maintained a robust trading network. Along with the Sultanate of Hobyo ruled by Sultan Yusuf Ali Kenadid, the Majeerteen Sultanate was eventually annexed into Italian Somaliland in the early 20th century, following the military Campaign of the Sultanates. Americas The term colonialism is normally used with reference to discontiguous overseas empires rather than contiguous land-based empires, European or otherwise. European colonisation during the 15th to 19th centuries resulted in the spread of Christianity to Sub-Saharan Africa, the Americas, Australia and the Philippines. Exploration and conquest of the Americas Christopher Columbus came to the Americas in 1492. Subsequently, the major sea powers in Europe sent expeditions to the New World to build trade networks and colonies and to convert the native peoples to Christianity. Pope Alexander VI divided newly discovered lands outside Europe between Spain and Portugal along a