Complex sentence: The conquest of the Middle East by Alexander the Great in the years from 331 BCE overturned centuries of Mesopotamian dominance and led to the ascendancy of Greek, which became the dominant language throughout the Seleucid Empire, but significant pockets of Aramaic-speaking resistance continued.
Split into simpler sentences: The conquest of the Middle East by Alexander the Great in the years from 331 BCE overturned centuries of Mesopotamian dominance and led to the ascendancy of Greek. This became the dominant language throughout the Seleucid Empire, but significant pockets of Aramaic-speaking resistance continued.