Early Buddhism

The term Early Buddhism can refer to two distinct periods, both of which are covered in a separate article:

The period of pre-sectarian Buddhism lasted until about 150 years after the death of Gautama Buddha. The various splits within the monastic organization went together with the introduction and emphasis on Abhidhammic literature by some schools. This literature was specific to each school, and arguments and disputes between the schools were often based on these Abhidhammic writings. However, actual splits were originally based on disagreements on vinaya (monastic discipline), though later on, by about 100 CE or earlier, they could be based on doctrinal disagreement. Pre-sectarian Buddhism, however, did not have Abhidhammic scriptures, except perhaps for a basic framework, and not all of the early schools developed an Abhidhamma literature.

Pre-sectarian Buddhism, also called "early Buddhism", "the earliest Buddhism", and "original Buddhism", is the Buddhism that existed before the various subsects of Buddhism came into being.

Some of the contents and teachings of this pre-sectarian Buddhism may be deduced from the earliest Buddhist texts, which by themselves are already sectarian.

The early Buddhist schools are those schools into which the Buddhist monastic saṅgha initially split, due originally to differences in vinaya and later also due to doctrinal differences and geographical separation of groups of monks.

The original saṅgha split into the first early schools (generally believed to be the Sthavira nikāya and the Mahāsāṃghika) a significant number of years after the death of Gautama Buddha. According to scholar Collett Cox "most scholars would agree that even though the roots of the earliest recognized groups predate Aśoka, their actual separation did not occur until after his death." Later, these first early schools split into further divisions such as the Sarvāstivādins and the Dharmaguptakas, and ended up numbering, traditionally, about 18 or 20 schools. In fact, there are several overlapping lists of 18 schools preserved in the Buddhist tradition, totaling about twice as many, though some may be alternative names. It is thought likely that the number is merely conventional.

...
Wikipedia