From the Arabs, the South Sudanese may have obtained new breeds of humpless cattle. Archaeologist Roland Oliver notes that the period also shows an Iron Age beginning among the Nilotics. These factors may explain how the Nilotic speakers expanded to dominate the region. There is also a myth told by the people of South Sudan that, some ethnic like Nuer and Dinka have migrated from West Africa specifically from modern day Senegal and Male. But that may have happened way back before the start of the 1st AD. The South Sudanese people through out history are cattle herders and they move from place to place in search of grassland and water which is always become Seasonal and which is always affected by existence of rainfall. Until about 1500 vast parts of South Sudan were controlled by speakers of Central Sudanic languages. A few Central Sudanic groups remain such as the Madi and the Moru. By the sixteenth century, the most powerful group among the Nilotic speakers were Shilluk, who spread east to the banks of the white Nile under the legendary leadership of Nyikang, who is said to have ruled the Shilluk c.1490 to c.1517. The Shilluk gained control of the west bank of the river as far north as Kosti in Sudan. There they established an economy based on cattle raising, cereal farming, and fishing, with small villages located along the length of the river. The Shilluk developed an intensive system of agriculture, and the Shilluk lands in the 17th century had a population density similar to that of the Egyptian Nile lands. One theory is that it was pressure from the Shilluk that drove the Funj people north, who would establish the Sultanate of Sennar. The Dinka remained in the Sudd area, maintaining their transhumance economy. While the Dinka were protected and isolated from their neighbors, the Shilluk were more involved in international affairs. The Shilluk controlled the west bank of the White Nile, but the other side was controlled by the Funj Sultanate, and there was a regular conflict between the two. The Shilluk had the ability to quickly raid outside areas by war canoe and had control of the waters of the Nile. The Funj had a standing army of armored cavalry, and this force allowed them to dominated the plains of the sahel. Shilluk traditions tell of King Odak Ocollo who ruled c. 1630 and led them in a three-decade war with Sennar over control of the White Nile trade routes.