Complex sentence: The Indo-Aryan Migration theory, which is part of the Indo-European migration theory, posits a migration from the Pontic Steppes into Europe, the Levant, south Asia and east Asia.
Split into simpler sentences: The Indo-Aryan Migration theory is part of the Indo-European migration theory. This theory posits a migration from the Pontic Steppes into Europe, the Levant, south Asia and east Asia.