A Study of the Buddha’s Travels is written by S. Dhammika. This book is about the only two of the great religious teachers who were successful during their own lifetimes were Mohammed and Gautam Buddha. Both had long teaching careers and both lived to see their respective religions firmly established. Prof. Basham has written that Buddhism was a minor religion until its adoption and promotion by King Asoka.
Basham bases his assumption on the fact that there is no archaeological evidence of Buddhism before Asoka’s time but this seems to me to be a rather weak argument. What physical evidence are wandering ascetics, which are what the Buddha’s disciples were, likely to leave? They established few permanent monasteries and those they did build were made of mud, bamboo and thatch. As for stupas, these did not become an important feature of Buddhist worship until about the 3nd century BCE.