Final answer:
Theravada Buddhism became popular in Southeast Asia as it subverted the caste system and was spread through trade routes, becoming an influential cultural force that shaped local politics, art, and architecture. Its adaptability and appeal to individual spiritual pursuits helped it coexist with local beliefs, leading to its adoption as the religion of the masses.
Step-by-step explanation:
Theravada Buddhism became the religion of the masses in Southeast Asia partly because it did not emphasize the caste system, which allowed it to be more attractive to people of lower social standings who sought spiritual liberation. The region’s trade routes facilitated the spread of Buddhism, and the creation of hubs for travel, learning, and commerce aided by that trade also contributed to its popularity. Theravada Buddhism, as the religion of the masses, was adopted due to several factors including its opposition to the caste system, the role of trade in spreading religious ideas, and the establishment of temples that served as critical hubs for cultivating the religion.
Distinguished from Hinduism and supported by local rulers for its ability to foster trade and community, as in the powerful kingdom of Srivijaya, Theravada Buddhism was seen as a path to enlightenment that focused on individual meditation and concentration. It became ingrained in the fabric of Southeast Asian societies, not just as a religious tradition but also as an influential cultural force shaping art, architecture, and political legitimacy as seen in landmarks such as Indonesia's Borobudur temple.
Theravada Buddhism's capacity to coexist with local traditions and to adapt to the socio-political context of Southeast Asian communities further contributed to its widespread acceptance and long-lasting influence in the region.