Ancient cultural region of the Tigris and Euphrates river system. The area was divided into Sumer (southeast) and Akkad (northwest) when the first Babylonian line of Amorite kings took power after 2000 BC. Largely because of the efforts of Hammurabi (r. c. 1792–50 BC), Babylonia gained regional hegemony but declined after his death; the Kassites from the east eventually assumed power (c. 1595) and established a dynasty that lasted some four centuries. After Elam conquered Babylonia (c. 1157 BC), a series of wars established a new Babylonian dynasty whose outstanding member was Nebuchadrezzar I (r. c. 1124–03 BC). Following his rule, a three-way struggle developed for control of Babylonia among Assyria, Aram (seeAramaeans), and Chaldea, in which the Assyrians ruled the area most frequently (9th–7th century BC). In the 7th–6th century BC the Chaldean Nebuchadrezzar II (605–562 BC) instituted the last and greatest period of Babylonian supremacy, conquering Syria and Palestine and rebuilding Babylon, the capital city. It was conquered in 539 BC by the Persian Achaemenian dynasty under Cyrus II and in 331 BC by Alexander the Great, after which the capital city was gradually abandoned.