Short answers, pulled from the story.
Theravada Buddhism arrived in Sri Lanka during the third century before the Common Era when missionary monk Mahinda spread the teachings of the Buddha. King Devanampiya Tissa reigned from 247 BCE to 207 BCE and established this faith as the state religion.
King Anawrahta of Burma ruled from 1044 to 1077 and played a central role in converting his kingdom to the Mahavihara school. Monks from Sri Lanka traveled to mainland Southeast Asia to establish Theravada as the dominant religious force between the eleventh and thirteenth centuries.
The Pali Tipitaka consists of three parts: the Vinaya Pitaka, Sutta Pitaka, and Abhidhamma Pitaka. The Abhidhamma Pitaka is believed to be a later addition dating from around the third century BCE onwards and was not recognized outside the Theravada school.
By the first century BCE the Pali Canon had been committed to writing for the first time preserving centuries of oral tradition. This written record became the foundation for what would become known as the Mahavihara tradition centered at the Great Vihara in Anuradhapura.
The Theravada Vinaya contains 227 monastic rules for bhikkhus while the Dharmaguptaka Vinaya has 253 rules. These differences arose from systematization and historical development centuries after the Buddha's death.