The commonly accepted period of earlier Vedic age is dated back to the second millennium BCE. After the collapse of the Indus Valley Civilisation, which ended c. 1900 BCE, groups of Indo-Aryan peoples migrated into north-western India and started to inhabit the northern Indus Valley. The Indo-Aryans were a branch of the Indo-Iranians, which—according to the most widespread hypothesis—originated in the Andronovo culture in the Bactria-Margiana area, in present northern Afghanistan.[note 1]
Some writers and archaeologists have opposed the notion of a migration of Indo-Aryans into India. Edwin Bryant and Laurie Patton used the term "Indo-Aryan Controversy" for an oversight of the Indo-Aryan Migration theory, and some of its opponents. These ideas are outside the academic mainstream.[note 2] Mallory and Adams note that two types of models "enjoy significant international currency" as to the Indo-European homeland, namely the Anatolian hypothesis, and a migration out of the Eurasian steppes. According to Upinder Singh, "The original homeland of the Indo-Europeans and Indo-Aryans is the subject of continuing debate among philologists, linguists, historians, archaeologists and others. The dominant view is that the Indo-Aryans came to the subcontinent as immigrants. Another view, advocated mainly by some Indian scholars, is that they were indigenous to the subcontinent."
The knowledge about the Aryans comes mostly from the Rigveda-samhita, i. e. the oldest layer of the Vedas, which was composed c. 1500–1200 BCE. They brought with them their distinctive religious traditions and practices. The Vedic beliefs and practices of the pre-classical era were closely related to the hypothesised Proto-Indo-European religion, and the Indo-Iranian religion. According to Anthony, the Old Indic religion probably emerged among Indo-European immigrants in the contact zone between the Zeravshan River (present-day Uzbekistan) and (present-day) Iran. It was "a syncretic mixture of old Central Asian and new Indo-European elements", which borrowed "distinctive religious beliefs and practices" from the Bactria–Margiana culture.[note 3]
Early Vedic period (c. 1500 – c. 1200 BCE)
The Rigveda contains accounts of conflicts between the Aryas and the Dasas and Dasyus. It describes Dasas and Dasyus as people who do not perform sacrifices (akratu) or obey the commandments of gods (avrata). Their speech is described as mridhra which could variously mean soft, uncouth, hostile, scornful or abusive. Other adjectives which describe their physical appearance are subject to many interpretations. However, some modern scholars such as Asko Parpola connect the Dasas and Dasyus to Iranian tribes Dahae and Dahyu and believe that Dasas and Dasyus were early Indo-Aryan immigrants who arrived into the subcontinent before the Vedic Aryans.
Accounts of military conflicts between the various tribes of Vedic Aryans are also described in the Rigveda. Most notable of such conflicts was the Battle of Ten Kings, which took place on the banks of the river Parushni (modern day Ravi).[note 4] The battle was fought between the tribe Bharatas, led by their chief Sudas, against a confederation of ten tribes. The Bharatas lived around the upper regions of the river Saraswati, while the Purus, their western neighbours, lived along the lower regions of Saraswati. The other tribes dwelt north-west of the Bharatas in the region of Punjab. Division of the waters of Ravi could have been a reason for the war. The confederation of tribes tried to inundate the Bharatas by opening the embankments of Ravi, yet Sudas emerged victorious in the Battle of Ten Kings. Purukutsa, the chief of the Purus, was killed in the battle and the Bharatas and the Purus merged into a new tribe, the Kuru, after the war.
Later Vedic period (c. 1100 – c. 500 BCE)
After the 12th century BCE, as the Rigveda had taken its final form, the Vedic society, which is associated with the Kuru-Pancala region but were not the only Indo-Aryan people in northern India, transitioned from semi-nomadic life to settled agriculture in north-western India. Possession of horses remained an important priority of Vedic leaders and a remnant of the nomadic lifestyle, resulting in trade routes beyond the Hindu Kush to maintain this supply as horses needed for cavalry and sacrifice could not be bred in India. The Gangetic plains had remained out of bounds to the Vedic tribes because of thick forest cover. After 1000 BCE, the use of iron axes and ploughs became widespread and the jungles could be cleared with ease. This enabled the Vedic Aryans to extend their settlements into the western area of the Ganga-Yamuna Doab. Many of the old tribes coalesced to form larger political units.
The Vedic religion was further developed with the emergence of the Kuru kingdom, systematising its religious literature and developing the Śrauta ritual. It is associated with the Painted Grey Ware culture (c.1200-600 BCE), which did not expand east of the Ganga-Yamnuya Doab. It differed from the related, yet markedly different, culture of the Central Ganges region, which was associated with the Northern Black Polished Ware and the Mahajanapadas of Kosala and Magadha.
In this period the varna system emerged, state Kulke and Rothermund, which in this stage of Indian history were a "hierarchical order of estates which reflected a division of labor among various social classes". The Vedic period estates were four: Brahmin priests and warrior nobility stood on top, free peasants and traders were the third, and slaves, labourers and artisans, many belonging to the indigenous people, were the fourth. This was a period where agriculture, metal, and commodity production, as well as trade, greatly expanded, and the Vedic era texts including the early Upanishads and many Sutras important to later Hindu culture were completed.
The Kuru Kingdom, the earliest Vedic "state", was formed by a "super-tribe" which joined several tribes in a new unit. To govern this state, Vedic hymns were collected and transcribed, and new rituals were developed, which formed the now orthodox Śrauta rituals. Two key figures in this process of the development of the Kuru state were the king Parikshit and his successor Janamejaya, transforming this realm into the dominant political and cultural power of northern Iron Age India.
The most well-known of the new religious sacrifices that arose in this period were the Ashvamedha (horse sacrifice). This sacrifice involved setting a consecrated horse free to roam the kingdoms for a year. The horse was followed by a chosen band of warriors. The kingdoms and chiefdoms in which the horse wandered had to pay homage or prepare to battle the king to whom the horse belonged. This sacrifice put considerable pressure on inter-state relations in this era. This period saw also the beginning of the social stratification by the use of varna, the division of Vedic society in Kshatriya, Brahmins, Vaishya and Shudra.
The Kuru kingdom declined after its defeat by the non-Vedic Salva tribe, and the political centre of Vedic culture shifted east, into the Panchala kingdom on the Ganges, under King Keśin Dālbhya (approximately between 900 and 750 BCE). Later, in the 8th or 7th century BCE, the kingdom of Videha emerged as a political centre farther to the East, in what is today northern Bihar of India and southeastern Nepal, reaching its prominence under the king Janaka, whose court provided patronage for Brahmin sages and philosophers such as Yajnavalkya, Uddalaka Aruni, and Gargi Vachaknavi; Panchala also remained prominent during this period, under its king Pravahana Jaivali.
By the 6th century BCE, the political units consolidated into large kingdoms called Mahajanapadas. The process of urbanisation had begun in these kingdoms, commerce and travel flourished, even regions separated by large distances became easy to access. Anga, a small kingdom to the east of Magadha (on the door step of modern-day West Bengal), formed the eastern boundary of the Vedic culture. Yadavas expanded towards the south and settled in Mathura. To the south of their kingdom was Vatsa which was governed from its capital Kausambi. The Narmada River and parts of North Western Deccan formed the southern limits. The newly formed states struggled for supremacy and started displaying imperial ambitions.
The end of the Vedic period is marked by linguistic, cultural and political changes. The grammar of Pāṇini marks a final apex in the codification of Sutra texts, and at the same time the beginning of Classical Sanskrit. The invasion of Darius I of the Indus valley in the early 6th century BCE marks the beginning of outside influence, continued in the kingdoms of the Indo-Greeks. Meanwhile, in the Kosala-Magadha region, the shramana movements (including Jainism and Buddhism) objected the self-imposed authority and orthodoxy of the intruding Brahmins and their Vedic scriptures and ritual. According to Bronkhorst, the sramana culture arose in "greater Magadha," which was Indo-European, but not Vedic. In this culture, kshatriyas were placed higher than Brahmins, and it rejected Vedic authority and rituals.