The Shingon (Tantric) tradition of Mahayana Buddhism arose in India in approximately the 6th century AD, although its roots go back many hundreds of years before that. It, too, adopted the position that none of the Hinayana (and now none of the Mahayana) was to be rejected.
If the world was indeed the body and the mind of Mahavairocana (Dainichi Nyorai), then all religious teachings possessed in some measure the Truth, and especially all Buddhist groups must possess this Truth in a greater or lesser degree. Tantrism began as a movement more concerned with the Practice of Buddhism than with any theoretical reformulation of doctrine.
The practice of Tantrism was primarily concerned with the means by, which once could attain Buddhahood, to supreme awakening in this very life. Since Tantrism was concerned with both the ritual and meditation practices leading to enlightenment, the Shingon tradition has developed highly complex and long rituals that monks and qualified laymen undergo to approach enlightenment. In general, Tantrism has been more concerned with practice than with doctrinal speculation.