After the Hittite destruction, Babylon was ruled by Kassites for 576 years. Next it was ruled by Elam, and then regained its independence for about three centuries. They were then conquered by the Neo-Assyrians. A century later they again became free, to form the Neo-Babylonian or Chaldean Empire. This constant conquest and re-conquest is partly due to geography. There are no natural boundaries except the rivers, and it is easy to get at the cities from north or south.