How did Taoism Begin?

how did it begin?

Someone invented it

Taoism began with the Chinese philosopher Lao Tze in the 6Th century BCE. Tao lived in the same time as Confucius. It is said that one day Lao Tze left his job and rode off west on an ox. At a mountain pass the guardian asked him to write down his teachings. This is how the sacred book of Tao (The Tao-Te-Ching) came to be written.

Taoism is practiced by about five million people in China, Japan, Malaysia, Hong Kong, Taiwan and Viet Nam. It is not uncommon for Taoism to be combined with Confucianism and Buddhism.

I don't believe anyone knows. Some cite the story of Lao Tzu (old man Tzu) who after years of working at the Royal Court was persuaded to write down his thoughts in the book we now call the Tao Te Ching.

But most likely Taoism developed many years before this out of Chinese folk religions.

Taoism as far as I am aware has never been a very unified religion, existing in 'philosophic', 'religious' and 'folk' strands and through numerous schools. Rather like (since Taoists like using water as a metaphor) a river fed by many small streams that in turn breaks into further streams at its delta with the sea. Hence the difficulty in pinpointing exactly when and how it arose.

As a Taoist myself I'd of course say that it's the practice of Taoism that matters, not how it began! But the Wiki article below might help a bit.
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To further elucidate on Katmandu's answer, no one really knows if Lao Tze (Laozi, Lao Tzu) ever really existed. Taoism is based on an amalgamation of ancient Chinese folk religions. Lao Tze was apparently the author of the book "Tao Te Ching" or "Daodejing", which translates to "Classic Way of Virtue". However scholars cannot agree whether Lao Tze wrote the book in the 6Th century BCE, the 3rd century BCE, or if he existed at all. One theory is that several authors compiled the book and attributed it to Lao Tze. Some legends have it that Lao Tze was a teacher to both Confuscious in China and Buddha in India. At any rate, Taoism was originally a philosophy until the second century CE when the Tang Dynasty accorded Lao Tze Divine status and made Taoism the official State religion. Of course later Dynasties chose other religions to be the Official Religion, and the number of adherents to Taoism dwindled.