When I took that orchestra from Garfield High School in Seattle on a tour of Kashima Shrine last July I had the opportunity to talk to the high priest there, and I learned a lot of things about Shinto. Some were things I had never heard before, others were additions and corrections to what I had learned elsewhere.
Shinto was originally a shamanistic faith (rather like Native American or Australian Aborigine religions) and its practitioners were exclusively women. Every village had a priestess (or order thereof) both to perform the necessary rituals and to consult the counsel of the spirits before any major undertaking. Quite often the high priestess was the true ruler of the tribe (something you can see in the movie Princess Mononoke ).
During the Asuka Period (5th to 7th century), when Buddhism was brought over from Korea and became firmly established, Shinto was literally absorbed into the "new" religion, considered separate yet part of it. When that happened, the original priestesses were eliminated (because Buddhism was strictly paternalistic in those days), and the Buddhist priests served dual roles. This continued until the two religions began to separate again after the end of the Heian Period. (Perhaps that's why Shinto priest robes look like Heian Period courtly dress!)
Even though it was more or less a distinct religion again, Shinto continued to be subservient to Buddhism until the Edo Period (late 16th to 19th centuries), when it was given new recognition by the shogun Ieyasu Tokugawa, who practiced any religion he could find (including Christianity, apparently) in order to give himself as much divine aid as possible. Tokugawa was the one who had Kashima Shrine fully restored as a pure shrine, as it had mainly served as a Buddhist/Zen monastery from the 7th century.
Interestingly, after the Meiji Restoration, when Imperial rule was restored, Shinto actually came to be the dominant Japanese religion again as the newly-empowered emperor was believed to be a Shinto deity (a direct descendent of the Sun Goddess Amaterasu-no-Omigami, to be exact). This continued until the end of World War II. Now it seems to be more of a mere custom than a religion people actually believe in and practice.
I had a Shinto wedding. The Heian Period courtly music they played was eerie!
- Moody Minstrel