Not just the Aryans, I would not agree that before coming of Aryans the whole of India was vegetarian. And there were invaders/migrants other than Aryans too. Much of the Persian influence was to the West of River Indus.
Achaemenid Empire (550330 BC), Macedonian Empire (330-323 BC), Seleucid Empire (312-63 BC), Parthian Empire (247 BC- 224 AD), Indo-Scythian Kingdom (200 BC400 AD), Indo-Greek Kingdom (180 BC10 AD), Indo-Parthian Kingdom (21130s AD), Western Satrap Empire (35405 AD), Kushan Empire (60240 AD), Sasanian Empire (224-651 AD), Indo-Sassanid Kingdom (230360 AD), Huna Kingdom (475576 AD).That is sort of new. No definite date for coming of Aryans, but they were comfortably settled in India in the late RigVedic time of Dasarajna war and drying up of River Saraswati. Therefore, prior to 2,000 BC.