Final answer:
During the first period of Buddhist expansion, Buddhism was dominated by the rules of the monastic discipline known as the Vinaya.
Step-by-step explanation:
During the first period of Buddhist expansion, the religion spread throughout India and was governed by the rules of the monastic discipline, known as the Vinaya. The Vinaya constitutes the regulatory framework for the monastic community of Buddhism, detailing the rules monks and nuns must follow. This framework helped to maintain the order and discipline essential for the monastic life, which is one of the cornerstones of Buddhist practice. As Buddhism spread, the influence of the Vinaya and other core elements like the Dharma, Sangha, and Bodhisattva ideals also extended, shaping the practice and expansion of Buddhism.