One More Council
The Fourth Buddhist Council probably was a synod of the emerging Theravada school, although there are multiple versions of this history, also. According to some versions it was at this council, held in Sri Lanka in the 1st century BCE, that the final version of the Pali Canon was put in writing for the first time. Other accounts say the Canon was written down a few years later.
The Emergence of Mahayana
It was during the 1st century BCE that Mahayana Buddhism emerged as a distinctive school. Mahayana possibly was an offspring of Mahasanghika, but there probably were other influences also. The important point is that Mahayana views didn't happen for the first time in the 1st century, but had been evolving for a long time.
During the 1st century BCE The name Mahayana, or "great vehicle," was established to distinguish this divergent school from Theravada/Sthaviravada school. Theravada was derided as "Hinayana," or the "lesser vehicle." The names point to the distinction between Theravada's emphasis on individual enlightenment and the Mahayana ideal of the enlightenment of all beings. The name "Hinayana" is generally considered to be a pejorative.
Today, Theravada and Mahayana remain the two primary doctrinal divisions of Buddhism. Theravada for centuries has been the dominant form of Buddhism in Sri Lanka, Thailand, Cambodia, Burma (Myanmar) and Laos. Mahayana is dominant in China, Japan, Taiwan, Tibet, Nepal, Mongolia, Korea, India and Vietnam.
Buddhism at the Beginning of the Common Era
By the year 1 CE, Buddhism was a major religion in India and had been established in Sri Lanka. Buddhist communities also flourished as far west as present-day Pakistan and Afghanistan. Buddhism had divided into Mahayana and Theravada schools. By now some monastic sanghas were living in permanent communities, or monasteries.
The Pali Canon was preserved in written form. It is possible some of the Mahayana sutras were written, or being written, at the beginning of the 1st millennium, although some historians put the the composition of most of the Mahayana sutras in the 1st and 2nd centuries CE.
About 1 CE, Buddhism began a vital new part of its history when Buddhist monks from India took the dharma to China. However, it would yet be many centuries before Buddhism reached Tibet, Korea and Japan.