Hindu synthesis in the context of "Iron Age in India"

Anatomically modern humans first arrived on the Indian subcontinent between 73,000 and 55,000 years ago. The earliest known human remains in South Asia date to 30,000 years ago. Sedentariness began in South Asia around 7000 BCE; by 4500 BCE, settled life had spread, and gradually evolved into the Indus Valley Civilisation, one of three early cradles of civilisation in the Old World, which flourished between 2500 BCE and 1900 BCE in present-day Pakistan and north-western India. Early in the second millennium BCE, persistent drought caused the population of the Indus Valley to scatter from large urban centres to villages. Indo-Aryan tribes moved into the Punjab from Central Asia in several waves of migration. The Vedic Period of the Vedic people in northern India (1500–500 BCE) was marked by the composition of their extensive collections of hymns (Vedas). The social structure was loosely stratified via the varna system, incorporated into the highly evolved present-day Jāti system. The pastoral and nomadic Indo-Aryans spread from the Punjab into the Gangetic plain. Around 600 BCE a second urbanization occured resulting in a new interregional culture; then, smaller janapadas (realms) were consolidated into mahajanapadas (great states). This period saw the rise of new ascetic movements and religious concepts, including the rise of Jainism and Buddhism. The latter was synthesized with the preexisting religious cultures of the subcontinent, giving rise to Hinduism.

Chandragupta Maurya overthrew the Nanda Empire and established the first great empire in ancient India, the Maurya Empire. India's Mauryan king Ashoka is widely recognised for the violent Kalinga War and his historical acceptance of Buddhism and his attempts to spread nonviolence and peace across his empire. This period marks the rapid dissemination of Śramaṇic religions.

Buddhism, which originated in India, gradually dwindled in that region starting in the 4th–6th century CE, and was largely ousted by Hinduism approximately by the 12th century, in a centuries-long process. Lack of appeal among the rural masses, who instead embraced religious rituals and beliefs developed during the Hindu synthesis, as well as Turkic invasions and dwindling financial support from trading communities and royal elites, were major factors in the decline of Buddhism in its Indian homeland. Across many centuries, Buddhism largely spread to other regions of Asia.

The total Buddhist population in 2010 in the Indian subcontinent – excluding that of Sri Lanka, Bhutan (both Buddhist majority states), and Nepal – was about 10 million, of which about 92.5% in India, 7.2% lived in Bangladesh and 0.2% in Pakistan.

Sanskritisation (or Sanskritization) is a process through which individuals or communities belonging to certain castes and tribal groups adopt the culture, values, lifestyles, and ritual practices of the dominant upper castes, with the aim of attaining upward social mobility and an elevated social status within the hierarchical structure of caste system of India. The phenomenon bears resemblance to the sociological concept of "passing". The term Sanskritisation was popularised in the 1950s by Indian sociologist and anthropologist M. N. Srinivas.

Sanskritisation has in particular been observed among mid-ranked members within caste hierarchy. It is considered an aspect of the wider historical and cultural process of Brahmanisation, which is the assimilation or alignment of local and regional Indian religious traditions with Brahmanism, leading to the Hindu synthesis and the formation of Hinduism, through a syncretic blending of diverse beliefs and customs into the Brahmanical fold.

Anatomically modern humans first arrived on the Indian subcontinent between 73,000 and 55,000 years ago. The earliest known human remains in South Asia date to 30,000 years ago. Sedentariness began in South Asia around 7000 BCE; by 4500 BCE, settled life had spread, and gradually evolved into the Indus Valley Civilisation, one of three early cradles of civilisation in the Old World, which flourished between 2500 BCE and 1900 BCE in present-day Pakistan and north-western India. Early in the second millennium BCE, persistent drought caused the population of the Indus Valley to scatter from large urban centres to villages. Indo-Aryan tribes moved into the Punjab from Central Asia in several waves of migration. The Vedic Period of the Vedic people in northern India (1500–500 BCE) was marked by the composition of their extensive collections of hymns (Vedas). The social structure was loosely stratified via the varna system, incorporated into the highly evolved present-day Jāti system. The pastoral and nomadic Indo-Aryans spread from the Punjab into the Gangetic plain. Around 600 BCE a second urbanization occurred resulting in a new interregional culture; then, smaller janapadas (realms) were consolidated into mahajanapadas (great states). This period saw the rise of new ascetic movements and religious concepts, including the rise of Jainism and Buddhism. The latter was synthesized with the preexisting religious cultures of the subcontinent, giving rise to Hinduism.

Chandragupta Maurya overthrew the Nanda Empire and established the first great empire in ancient India, the Maurya Empire. India's Mauryan king Ashoka is widely recognised for the violent Kalinga War and his historical acceptance of Buddhism and his attempts to spread nonviolence and peace across his empire. This period marks the rapid dissemination of Śramaṇic religions.

Hinduism and Buddhism have common origins in Ancient India, which later spread and became dominant religions in Southeast Asian countries, including Cambodia and Indonesia around the 4th century CE. Buddhism arose in the Gangetic plains of Eastern India in the 5th century BCE during the Second Urbanisation (600–200 BC). Hinduism developed as a fusion or synthesis of practices and ideas from the ancient Vedic religion and elements and deities from other local Indian traditions.

Both religions share many beliefs and practices but also exhibit pronounced differences that have led to significant debate. Both religions share a belief in karma and rebirth (or reincarnation). They both accept the idea of spiritual liberation (moksha or nirvana) from the cycle of reincarnation and promote similar religious practices, such as dhyana, samadhi, mantra, and devotion. Both religions also share many deities (though their nature is understood differently), including Saraswati, Vishnu (Upulvan), Mahakala, Indra, Ganesha, and Brahma.

Hinduism is the largest religion in South Asia with about 1.2 billion Hindus, forming just under two-thirds of South Asia's population. South Asia has the largest population of Hindus in the world, with about 99% of all global Hindus being from South Asia. Hinduism is the dominant religion in India and Nepal and is the second-largest religion in Bangladesh, Pakistan, Sri Lanka, and Bhutan.

Indo-Aryan migrations brought the Indo-Aryans to South Asia, where they compiled and composed the Vedic corpus during the Vedic period (ca. 1500-500 BCE) across present-day Northern India, Pakistan and Afghanistan. The subsequent period, between 800 BCE and 250 BCE, was "a turning point between the Vedic religion and Hindu religions", and a formative period for Hinduism, Jainism and Buddhism. The Epic and Early Puranic period, from c. 250 BCE and 500 CE, saw the onset of the Hindu synthesis, followed by the classical "Golden Age" of India (c. 350 - 650 CE), which coincides with the Gupta Empire.