Original: Originally inspired by 17th, 18th and 19th century Romantic movements, modern Druidism was based upon theories about the Iron Age Celtic druids which are no longer considered to be historically accurate.
Simplified: Originally inspired by 17th, 18th and 19th century romantic movements, early neo-druidism was based upon largely historically incorrect depictions of the Iron Age Celtic druids, and has no direct relation to the ancient Celts or their culture.