Complex sentence: His victories during the Naderian Wars briefly made him West Asia's most powerful sovereign and possessing over what was arguably the most powerful empire in the world, but his empire and the Afsharid dynasty he founded quickly disintegrated after he was assassinated in 1747.
Split into simpler sentences: His victories during the Naderian Wars briefly made him West Asia's most powerful sovereign over one of the most powerful empires in the world at that time. However, his empire and the Afsharid dynasty he founded quickly disintegrated after he was assassinated in 1747.