The Aryan conquest of North India was a process of gradual institutional assimilation and sociocultural integration between invading barbaric hordes and their more civilized pre-Aryan slaves.

The Mahabharata, whose epic core probably reflects Indian life at around 1000 BC, starts with King Santanu's love for the beautiful goddess Ganga, whom he marries. This symbolizes the Aryan advance east of the Doab into the Gangetic plain.

Several elaborate sacrifices, designed to consecrate roayalty, appear in Bramana commentaries on the Vedas, composed from about 1000 BC to 700 BC, attested to the growth of significance for kingship.

The Satapatha Brahman allegorically relates the eastward expansion of the Aryans as the the spread of Agni's divine fire.
Religious law called dharma dictated proper behavior for all within the kingdom.

The entire Ramayana may be read as an allegory of Aryan and pre-Aryan conflict, culminating in the conquest of the south.
Such a process of expansion, settled agricultural production and pluralistic integration of new peoples led to the development of India's uniquely complex system of social organization, which was labled the caste system by the Portuguese.

Plough and irrigation agriculture greatly increased the food supply available to Aryan settlers, permitting rapid expansion of India's population as a whole and the growth of extended family units within villages as well as towns.

Upanishadic mystics, masters of revealed Vedic scripture, represented the orthodox intellectual revolt against brahmanism that emerged in the eastern Gangetic plain in the 8th century BC. Upanishads( which means "to sit down in front of") had a three-fold quest; (1) From the unreal lead me to the real, (2) From darkness lead me to light, (3) From death lead me to immortality.
Upanishads may be ancient links to Taoist beliefs practiced in Mesopotamia.

Their belief system includes references to the cosmic soul equating with the individual soul. This is identical to the Taoist belief system and one of the few, if any major belief systems that mirror the Taoist system. Also the concept of controlling ourselves through understanding these cosmic forces is also very Taoist.

In a deer park at Sarnath, on the outskirts of Kasi, the Buddha was believed to have set his "wheel of the law" (dharma) in motion in 527 BC by preaching his first sermon (which included the four noble truths)`` after achieving enlightenment.
The Buddha spent the next 45 years of his life teaching these four noble truths to disciples who gathered around him in such numbers he was able to establish a monastic "order" (sangha).

Members of the sangha pursued a rigorous course of "right discipline" (sila), yogic concentration and thoughtful study in their search for nirvana.

The various sects of the sangha would lead to schisms within Buddhism that are prevalent to this day.
Buddha's final message was to be yourself and trust yourself. He did not set up his sangha to be "official" priests to distribute "canon law" or to assemble in "official temples". This is an obvious rebuff to later institutionalization of Buddhism and more in line with the Taoist model of the individual having to find his own way without being told what to do.

Courtesy --- CHAITANYA