The Samaritan Schism
Lawrence H. Schiffman, From Text to Tradition, Ktav Publishing House, Hoboken, NJ, 1991.
Throughout the Second Commonwealth Judeans and Samaritans were engaged in intermittent conflict. Many scholars, on the basis of studies of the Samaritan Pentateuch and the Samaritan script, have concluded that the schism should be dated to the building of the Samaritan Temple on Mount Gerizim late in the Persian period and its destruction by the Hasmonean king John Hyrcanus in 128 B.C.E. These scholars maintain that the officials of Samaria who opposed the rebuilding of Jerusalem cannot be identified with the later Samaritan sect. This distinction seems to be overdrawn. Granted that the schism was the result of a long process, its earliest stages are to be observed already in the early years of the Persian period.
The Samaritans were a mixed people, made up of Israelites who had not been exiled when the Northern Kingdom was destroyed in 722 B.C.E. and people of various foreign nationalities whom the Assyrians had resettled in the area in an attempt to ensure that Israels national aspirations could not again come to the fore. This mixed group had adopted a syncretistic form of Judaism that combined old northern traditions with those of the resettled nations. When work began on the Temple, the Samaritans approached the Jews to join in the project. The Judeans rejected the Samaritans because of their questionable descent......
It wasn’t just questionable descent but actual practice. Many had converted and the rabbis at that time thought their conversions were genuine until it was discovered that they were not. Those conversions were then ruled as invalid and the Samaritans have considered non-Jews since that time.