In the 1st millennium AD, from the Vedic Traditions, Hinduism was developed into the long-established traditions we see today. Around the same time when various Vedic Traditions were dominant in India, Tantra was developed; Inspired by the Vedic Tradition but more from its rituals such as yogic and meditative traditions which were also being developed in Buddhism and Jainism. A core part of each of these religions or traditions were sutras - principal texts. A sutra is a thread of thought, a particular line of thinking so if a sutra is a single thread of thinking, then a tantra is the whole system of thought. Tantras were teachings that could only be taught directly by a teacher to a student, but soon enough there were scriptures.
In the Kashmir Valley where the Tantras originally flourished, workings of ancient religious traditions worshipping Śiva and Śakti — Śiva as the essence of consciousness and Śakti as the essence of power, were already in place which later loomed into the Vedic Culture and Buddhism. The teachings gained popularity throughout India, especially within the strong middle class. This portion of the population was left out of the caste conscious religions of Vedic origin and monastic-male Buddhism. These were the two major religions in India at that time, Tantra offered a third alternative for those left out of the other two. A priestly class or monastic tradition had no place in this ancient tradition. These teachings honored the feminine as the heart of good teaching and considered women as the most powerful and influential teachers. All of the teachings, which influenced other religions and traditions, came to be known as Tantra. Thousands of teachers solidified into the core of Tantra and streamlined the teachings.
These teachings were spirited and taught that enlightenment was available in this life, not through reincarnations. The vague concept of nothingness in Buddhism was clarified as universal and ubiquitous consciousness. In Buddhism, the physical world is seen as an illusion, rather in this system, there is no difference between the material world and spiritual. It believes in the system of nondualism, in the sense that one’s true self (pure awareness, the Divine) exists in all particles of the universe. We perceive everything as duality around us, good and evil, boy and girl, hot and cold, this system believes that these illusions are created by our Ego, when, in fact, the opposites are considered the same in the universal consciousness. The established nature that defined tantra included: One on one student-teacher relationship, mindfulness, ritual as a means of deepening awareness, rejection of illogical religious and cultural rules, acceptance regardless of caste, nationality, language, and gender, a belief in body and the sensual experiences of the body as part of the path to the divine — not as a distraction from the divine.
THE REMAINS OF TANTRA
The original traditions of Tantra mostly died out around the 1100s, when Islam arrived in India. The influence of tantra extended to Hinduism, Buddhism, with a special and distinct survival in Vajrayana Buddhism of the Himalayas. It was preserved in a diminished form, however, in three different schools, the best-known being Vajrayana Buddhism, which was practiced in the Himalayas, and then spread to other parts of the East. The other two are the Brahmanic Sri Vidya lineage of southern India and Hatha Yoga. Tantra was seen as a spiritual practice independent of any particular religion, but adaptable to all.
You may have heard that Tantra is full of obscenities or that it has something to do with black magic. As a matter of fact, Tantra involves practices such as yoga, meditation, and the reading of sacred texts - elements that are common in other religions. Different traditions within Tantra choose to focus on different combinations of these practices, but they are certainly not focused on practicing any ‘dark arts.