The Aryans started moving between 1000 BC and 600 BC from the north-west and Punjab regions to the ganga-Yamuna plains. The Sama Veda, Yajur Veda, Atharva Veda, the Upanishads and the Mahabharata were created after the Rig Veda, hence are called ‘Later Vedic’.
In the Vedic period, the society was divided in to four groups or Varnas i.e. Brahmins, Kshatriyas, Vaishyas and Shudras as per the occupations. This Varna system was flexible and in the later Vedic period, the Varna of a person was decided on the basis of his birth. In spite of the huge following of the Varna system, many people opposed it.
In the early Vedic period, a Raja was elected by the people. However, later this system started fading and powerful men established their own kingdoms declaring themselves as Raja. They would perform the ritual of Ashwamedha or horse sacrifice to declare their supremacy.
In this ritual, a horse guarded by the Raja’s men would be left loose to wander in the neighboring kingdoms. If any Raja would stop the horse from entering his kingdom, he would have to battle with the Raja owning the horse. Nevertheless, if a Raja allowed the horse to enter his kingdom, it meant that he has accepted the supremacy of the Raja who owned the horse.
The Ashwamedha Yagnya was performed by specially trained priests who were later rewarded by the king. After the horse sacrifice, the king was declared as the most powerful in the presence of all the kings who accepted his supremacy. All these kings would give the Raja lavish gifts, including the Vaishyas. The Raja’s charioteer narrated incidents of the Raja’s exploits in the battlefields.
The extended regions of the Raja were called Mahajanapadas, comprising the forfeited kingdoms. By 600 BC there were around 16 Mahajanapadas i.e. Avanti, Anga, Magadha, Vajji, Kosala, Panchala, Kuru, Gandhara, Assaka, Cheti, Kamboja, Kasi, Matsya, Malla, Shurasena and Vasta.
In order to build the forfeited territories and pay the soldiers and labors, the king introduced the collection of taxes rather than depending on the gifts. The taxes depended on the occupation of the people.