Tantra is about the catalysis and acceleration of awareness. Tantra is not bound to any particular deity system, philosophy, cultural background or teaching modality.
Tantra is religion at it's liveliest. It has the passionate love of truth that most of the established religions started with. It has standards, views on what constitutes a worthwhile teaching, and ongoing, responsive quality control.
Sometimes, a teaching grows from previous teachings. Sometimes, a patriarchal lineage happens, a disciple or two of each generation completing their path in comfortable timing.
More usually, the appearance, the illusion of a patriarchal lineage and the development/revelation of teachings appropriate to the times has been managed from behind the scenes by Dakinis.
Often, Tantra had to present itself in a form that was alluring or scary to the surrounding culture. Sometimes it had to disappear. Sometimes, it had to infiltrate the prevailing organised religions.
Some branches did not develop, either pruned through losing the support and acknowledgment of Dakinis or just failing to produce capable teachers for a few generations.
Sometimes this was ugly, disciples becoming focused on a particular characteristic of (or attributed to) their historic guru and emulating that characteristic in stupid and excessive ways as only men can. Examples include (in increasing order of severity) ritual mutilation of the penis, obsessions with ejaculation and sexual repression.
Sometimes it was beautiful, the disciples preserving yoga exercises, dances, rituals, books, attitudes and methods for later generations and fresher lineages to borrow from.
The treasures of ancient tantra have been reaching the West for a long time. Gems like the Vigyan Bhairav Tantra and the poems of Rumi . These and the other gifts of history have contributed much to the development of Western Tantra. Recently, Daniel Odier's Tantric Quest, translating the understanding of Kashmir and Judith Simmer Brown's Dakini's Warm Breath urge a more complete, more mature understanding.
Tantra is always a fresh awareness, an arising of new understanding. Tantra is always at the beginning (a teacher and a few students) stage of development as a religion. One of the oldest and wisest sayings in Tantra is "Stay at the beginning." This applies at least as much in tantric practice and teaching as it does in making love.