Tendai, Shingon, Kegon etc are Japanese schools based on the Chinese sects of Mahayana Buddhism. But most of these sects involve central rituals, esoteric practices, mantras and probably Yoga like practices (Mudras?). So technically these also come under "Tantra"? If not, what is the difference between Tantra and these practices? Or are these standard Mahayana Buddhism (unlike the wrong conclusion that Mahayana only constitutes meditational, devotional and scholarly practices?)?
It appears that most of Tibetan Buddhism was "Created" under the rule of the Palas in India and that this variety of Siddha tradition is a direct evolution of the Tantric like practices that had already started emerging in standard Mahayana Buddhism of the earlier era when these were exported as far as Japan.
Could Shingon be characterized under "Vajrayana"?