2000 BCE-1500 BCE: A period of flooding and invasion in the Indus valley, caused by the invasion of the Yehnn (Aryans). They defeat the Harappan culture, but are forced to consult them to help rebuild the civilization. (Please note that Aryan Invasion Theory is considered discredited in real life.)
Aryans arrive in India. India adopts caste system. Nagah are considered to be of the two highest castes.