The Tao that can be spoken is not the true Tao!
However, apart from being facetious (sorry, couldn't resist), the hidden spread of Taoism began with the fusion of the Buddhas teachings with Tao in the form of Ch'an Buddhism in China. In Japan this resulted in Zen which, being very popular with the non religious heads of the beat generation, gradually took root in the USA amongst people who had turned away (for very good reasons) from traditional religion but who were still very interested in finding a spiritual path which could accept the all in one and the one in all without having to get into the whole God trip or the subsequent schizoid relations with reality which the people of the book (Jews, Muslims and Christians) seem particularly prone to. The 'spread' of Taoism is hard to define as there are also the polar variants which have little to do with enlightened being but are more concerned with propitiating the gods for good harvest, divination, success in the market place, a happy marriage etc. A bit like modern day American Christianity. May your understanding of the indescribable grow as your ego diminishes. That seems to me to by how it spreads. Hope that's helpful. Gerry
PS How does the Taoist master like his hot dog?
One with everything!