Complex sentence: The Elamite king fled to the mountains and Sennacherib plundered his kingdom, but when Sennacherib withdrew Elam put yet another rebel leader, Mushezib-Marduk, on the Babylonian throne.
Split into simpler sentences: The Elamite king fled to the mountains and Sennacherib plundered his kingdom. When Sennacherib withdrew, Elam put another rebel leader, Mushezib-Marduk, on the Babylonian throne.