Buddha's teachings started to small groups, multiplied out to very large audience.
Royal Support
King Bimbisara and Ajatasattu of Magadha and king Pasenadi Kosala of Kosala became the main patrons of Buddhism.
Personal Qualities of Buddha
family background
personal appearance
virtuous conduct
politeness
knowledge and understanding
His presentation of the Dhamma involved both his communicative skill and intellectual skill.
Different methods: round-about and direct
Approach
People were not forced to accept it without inquiry.
Freedom of investigation was highly valued in Buddhism.
It made an open invitation to all to come and see the truth of it.
Step-by-step approach. Anyone at any level can start the path.
Dedication by Sangha to propagation of Dharma
All members viewed equally - no caste, no gender discrimination
Support by "higher ranks"
Gifts of land, etc. by wealthy and kings