The mountain that trained everyone
Tendai, established by Saichō on Mount Hiei in the early Heian period, became the training ground of almost every founder who came after. Shingon, established by Kūkai, provided the court with esoteric ritual. Both remained powerful throughout the medieval period and both exist today.
What happened in the Kamakura period was not that these were replaced, but that men trained in them left to teach something simpler.
The Kamakura schools
Hōnen, who lived from 1133 to 1212, taught that reciting Amida's name is enough. Shinran, 1173 to 1263, took that further: salvation is Amida's work and not ours, so even the recitation is a response rather than an achievement. He married, had children, and called himself neither monk nor layman. The order that grew from him, Jōdo Shinshū, is the largest Buddhist body in Japan today.
Eisai and then Dōgen, 1200 to 1253, brought Chan lineages from China as Rinzai and Sōtō Zen. Dōgen taught shikantaza, just sitting, and insisted that practice is not a means to awakening but its expression. Nichiren, 1222 to 1282, taught the title of the Lotus Sūtra as the whole of practice, and attacked the other schools with a directness that got him exiled twice.
What followed
Zen's patronage by the Ashikaga shoguns shaped tea, ink painting, gardens and nō drama, which is why Japanese aesthetics and Buddhism are so hard to separate. Pure Land congregations became mass movements, and for a time the Ikkō-ikki leagues governed provinces of their own.
Under Tokugawa rule from 1603, every household was registered at a temple. That secured Buddhism's place in Japanese society and tied it to funerals and ancestors, a role it still carries. Hakuin, 1686 to 1769, revived Rinzai kōan training from inside that settled world.
Why it matters
Several of these schools remain central to Japanese Buddhism today.
History and tradition
What historians can say
Unusually well documented for medieval religion: the founders left substantial writings, and temple and government records survive. The convenient label Kamakura Buddhism has been criticised by historians, since these movements were small in their founders' lifetimes and became dominant only later.