Complex sentence: Whether these remnants were the ancestors of the Huns is still a controversy among some present-day historians especially the western, all have to agree that a power vacuum was left on the Mongolian steppes.
Split into simpler sentences: Whether these remnants were the ancestors of the Huns is still a controversy among some present-day historians, especially in the West. All must agree that a power vacuum was left on the Mongolian steppes.