The Great Plains Indian Trading Networks encountered by the first Europeans on the Great Plains were built on a number of trading centers acting as hubs in an advanced system of exchange over great distances. The primary centers were found at the villages of the Mandan, Hidatsa and Arikara, with a surplus of agricultural produce that could be exchanged. Secondary centers were found at the villages of the Pawnee, Kansa and Osage on the central plains, and at the Caddo villages on the southern plains. The Dakota rendezvous was an important annual trading fair among the Sioux. European demand for fur changed the relations of the plains, increased the occurrence of war, and displaced several Indian nations that were forced away by the Sioux coming from the east. On the northern plains, Europea