Complex sentence: The Postclassical Era, also referred to as the Medieval period or, for Europe, the Middle Ages, begins around 500 CE after the fall of major civilizations, covering the advent of Islam.
Split into simpler sentences: The Postclassical Era is also referred to as the Medieval period, or in some cases the Middle Ages (although this usually refers exclusively to Europe). It begins around 500 CE after the fall of major civilizations, covering the advent of Islam.