Complex sentence: In 678 BC, Deioces united the Median tribes of Media and made the first Iranian empire, his grandson, Cyaxares managed to unite all Iranian tribes of Ancient Iran and made his empire a major power.
Split into simpler sentences: In 678 BC, Deioces united the Median tribes of Media and made the first Iranian empire. His grandson, Cyaxares managed to unite all Iranian tribes of Ancient Iran and made his empire a major power.