The history of Tantra, how it has shifted and travelled through the lands and times is a beautiful journey that one must explore themselves to come to terms with the true ancient truths of the tantras. Through Hinduism, Jainism, Buddhism, the Vajrayana traditions and other ancient eastern religions the studies of tantra are mentioned and magnificently activated in ancient texts and teachings and in the tops of tibet.
Tantra is a way of life, thousands of years old.
I highly recommend continuous self study from various ancient sources far and wide to attain a vast and broad perspective on such an ancient connection, the web of tantra and its true meaning.
There are ancient book recommendations within The Great Library that should assist.