By controlling the trade routes with their powerful military forces, these empires were able to dominate neighbouring states. The Sudanic empires also became centres of Islamic education. Islam had been introduced in the western Sudan by Muslim Berber traders from North Africa; it spread rapidly after the conversion of many important rulers. From the 11th century, by which time the rulers of the Sudanic empires had embraced Islam, it spread south into the northern areas of contemporary Ivory Coast.