The ED was preceded by the Jemdet Nasr and then succeeded by the Akkadian period, during which, for the first time in history, large parts of Mesopotamia were united under a single ruler. The entirety of the ED is now generally dated to approximately 2900–2350 BC according to the middle chronology or 2800–2230 BC according to the short chronology. The ED was divided into the ED I, ED II, ED IIIa, and ED IIIb sub-periods. ED I–III were more or less contemporary with the Early Jezirah (EJ) I–III in Upper Mesopotamia. The exact dating of the ED sub-periods varies between scholars—with some abandoning ED II and using only Early ED and Late ED instead and others extending ED I while allowing ED III begin earlier so that ED III was to begin immediately after ED I with no gap between the two.