Hinduism (vedic tradition) started with creation, when Brahma was handed the Vedas as the body of knowledge to administer the creation function in the Universe. In that, it exists beyond just earth in other life-sustaining planets in the Universe. Historically, on earth, it has existed since creation of life on earth.
The root of Hinduism is in Dharma. Dharma is a mix of morality, virtue, integrity, conduct, physical and metaphysical concepts. E.g. it’s the dharma of water to wet a material, as is the dharma of fire to burn, or the dharma of Earth to go around the Sun. Dharma has always existed. Therefore, the metaphysical underpinnings of Hinduism have always existed.
Politically speaking, the term Hindu became prevalent to describe the civilization that lived in the subcontinent between the Himalayas and Indian Ocean. The identity of the people was termed Hindu by the conquerors from the West–Romans, Turks, Arabs, Persians, Mongols, and the British.
Hinduism as a philosophy has been well-formed at least for 5000 years, it has moulded as a political identity only in the last 1000 years since the Islamic conquests of India started in about 1100 AD.
Other reading material: https://houseoflac.wordpress.com/2018/02/14/what-is-dharma/
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Contributor: Rajeev Singh
Location of this post (12d): https://www.hinduspeakers.org/ufaqs/in-what-historical-context-did-hinduism-emerge/