Aryo-Dravidian Synthesis 
The post Vedic period saw the river  Saraswati dry up with the centre of Aryan power shifting to the banks  of the Ganga. This period (i.e. around 1200 b.c. to 700 b.c.) saw the  synthesis of Aryan and Dravidian cultures. Modern day Hinduism is a  product of these two cultures. The fusion took place in North India.
The Aryans were virile and  aggressive but their material culture was not as advanced as that of  the Dravidians. They readily adopted the good things. Marriages  between aryans, dravidians, asuras and nagas were common. The rishis  kept on spreading Aryan values, culture, institutions, traditions  amongst all, developing in them a sense of unity, continuity and a  collective action in social and cultural spheres.
Social groups who did not wholly  conform to the Aryan way of life were called the Shudras. The belief  that Shudras were wedded to social inferiority is a myth.  Untouchability as we know in recent ages was unknown during this  period. The four castes was not a rigid hereditary institution  as is today. Many of the Mahabharata heroes had mixed parentage.  Krishna attributed caste to qualities and action of men and not by  birth.
At the end of article are links to Demystifying Caste and how Different regions of India  contributed to Indian religious thought. 
With the end of the Vedic age, the  mantras were invested as divinity. Thus the Vedas became the source  of inspiration and direction for future generations. The other  institution that can be traced to Veda Vyas is the Tirth Cult,  the magnetic force that attracts people from Kerala or Kashmir to  have a dip in the holy Ganga. The concept of having a holy dip in the  river Ganges was a tradition that carried on from generation to  generation and served as a great unifying factor amongst all Indians.  To Vyasa we also owe the Mahabharata. There might not be a single  Indian child who has not heard of this epic. The T.V. serial on the  same only increased its popularity. A number of children who were  born between 1988 and 1990 were named Karan. In a sense the serial  reminded us of our glorious tradition, culture, and became a unifying  factor, a ‘sense of triumph’ as Munshiji put it. 
The Bharata war happened around 1200  b.c. The battle of Kurushetra lasted for eighteen days. The epic has  left two lasting memories on the Indian pshcye. Vyasa the learned  seer, the savior of the Vedas and Krishna the warrior and statesmen.  One taught Dharma and the other upheld it.
Now let’s look at Aryan  Dravidian syntheses
The Aryan society was patriarchal  like the Dravidian one. Polygamy was accepted as against monogamy  favored by the Aryans. Shiva, the Dravidian god known to the Harappan  culture was first identified with Vedic Rudra. Vedic gods Indra,  Varuna, Agni, and Surya took a subordinate place. Ma, the mother  goddess of the early Mediterranean people became the consort of Shiva  assuming the name of Parvati in the process. On the other hand, the  Vedic god Vishnu became popular and shared with Shiva the leadership  of the Pantheon.
The Vedic homa got replaced with  Dravidian puja, the offering of leaves, flowers to gods. Spirit of  tolerance and non-violence were new values that evolved as a result  of the impact and the tapas (explained above). The post Vedic period  gave a new shape to Rita, Satya, Yajna and Tapas.
First, the Cosmic Order, Rita, had a  new form ie the Supreme- Ishawara or Brahman, pervading as a  Reality standing above all that is and that is not. In simple  language it means,  believing that the cosmic order was the mother of  all creation. We started believing there was a Supreme ie God who was  responsible for all that is and that is not.
Secondly, the cosmic order in one of  its aspects is the Law of Evolution. Through it the supreme self  passes from lower things to higher things till he achieves  realization i.e. man’s attaining conscious oneness with it. In  human beings it works through three important laws i.e. law of karma,  law of moral causation and yoga.
According to the Law of Karma, the  atman or soul takes several births on its way to realization.  The  Law of Causation is an elaboration of the yagna (one of the Aryan  socio-religious institutions) aspect of Rita. Through it is possible  for man to reduce the number of times he is reborn by offering to  give up his ego and by taking vows of non-violence, truth, and  non-possession amongst others. 
Third, is Yoga, the  elaboration of the Tapas aspect of Rita.  It is practiced through  intensely pursued self-discipline. 
Man is a divine essence with supra  physical destiny which he can realize and then achieve through truth  and self-discipline. Self-realization implies two inter-dependant  processes, one is surrendering of one’s ego and other the  individual self is broadened into a universal self. 
When we exercise self-control over  mind and body, energy that would otherwise have been spent  unproductively gets released and brings the individual in touch with  the beautiful aspect of the absolute. This is when it takes the shape  of love, bhakti. Faith in the spiritual power, generated by this   energy of love, became one of the fundamental values of Indian  culture.
The Absolute descend on earth in  human form as an avatar; an aspirant by can attain him by complete  surrender of ego. In the post–Vedic period, this faith appears to  have grown. Thus at some point Naranya (sage), Vasudeva and Vishnu  became Hari, the Supreme Lord. In chalpter 11 of the Gita, Arjuna  sees in Krishna a god of gods, the protector of dharma, the presiding  deity of the cosmic order etc. At the same time he sees in Krishna,  Vasudeva who had taken birth to re-establish dharma. He is the love  aspect of God in whom one can live only through single minded  devotion. 
In this way, the realization of the  beauty aspect of the Cosmic Order through Love became one of the  fundamental values of Indian culture. Now I understand why my  temple pandit says, devotion to and faith in God are very important  if you want to be close to him. 
In order these values, revolving  around the Central Idea, were translated into Life a whole  superstructure of traditions, norms of conduct was reared. Social and  economic life was molded in a manner to find fulfillment by living up  to the Central Idea.
This chapter is important for all  those politicians and individuals who have created the Aryan and  Dravidian divide. Surely, they fought wars but the product of that  synthesis is what modern day Hinduism is all about. Some scholars  have tried to compare Islamic, Christian invasions with the so-called  Aryan invasion. Even though invasions enriched us in many ways, they  destroyed our culture and civilization. Conversely, the  Aryan-Dravidian synthesis helped both grow and blossom. Note that  Shivji is worshipped in Gujarat, Rajasthan, Kashmir, Tripura and even  in Arunachal whilst Vishnu Bhagwan is worshipped at Tirupati and  Trichy in Tamil Nadu. This north-south divide is a creation of vested  interests. 
There was racial fusion between  Aryans and non-Aryans. Veda Vyas was the son of a fisher girl.  Balarama, Krishna’s brother married the daughter of Kakudmin, who  belonged to a race from Saurashtra that existed long before the  Aryans came. 
Importantly, the chapter explains  the new shape of Rita, the cosmic order into Supreme Lord, the Law of  Karma and Causation, Yoga; it also explains how did Faith become a  fundamental value of Indian culture and the concept of Avatars.