- The Indo-Greeks (successors of Alexander's empire in Bactria) were among the earliest foreign invaders in this sequence, arriving from the 2nd century BCE onwards. - The Sakas (Indo-Scythians) followed the Greeks, starting their invasions from around the 1st century BCE. - The Kushans, originating from Central Asia, arrived later, establishing their empire in the 1st century CE, succeeding parts of the Saka and Parthian territories.