I've always thought that the term Samaritans in the Bible was referring to all inhabitants of northern ten tribe kingdom of Samaria right after the division of united Israel (after king Solomon's death). I got interested more about them when reading the account in John chapter four where Jesus spoke with a Samaritan women near a well revealing that he is the foretold savior of world. I got intrigued by the fact that Jews in Jesus time looked down upon Samaritans. If Samaritans were simply from northern ten tribe kingdom then why would Jews look down upon their own brothers and relatives? So I thought I would do some personal study on this.
Until the time of Solomon all Israel was under a united monarchy with one king ruling from Jerusalem. The division as pronounced by Jehovah's prophet Ahijah happened during the time of Solomon's son Rehoboam. God was displeased by the presumptuousness of Rehoboam in his later years when he abandoned pure worship and led his own tribe Judah in to a course of badness prevalent among neighboring nations (1 Kings 14:22-24). So it came about that Israel was split in to two kingdoms with only the two tribes of Benjamin and Judah in south giving allegiance to rulers from David's offspring and remaining ten tribes in north (Samaria) under a different king Jeroboam, one of Solomon's officers (1 Kings 11:29-31). It can be said that majority of the prophetical books in "old testament" (Hebrew/Aramaic scriptures) starting from the book of Isaiah is dealing with God's message to unfaithful people in both kingdoms that unless they turnaround they will be taken as captives for their sins. But people in both kingdoms willfully continued practicing what was bad.
The destruction of ten tribe northern kingdom of Samaria happened in 740 BC when king Shalmaneser V of ancient Assyria invaded and took most of them as captives. Later in 607 BC the two tribe kingdom of Judah was also invaded and taken as captives by Babylonians under king Nebuchadnezzar II until their liberation from exile by the decree of Mede Cyrus the Great in 537 BC.
Coming back to my original question on the origin of Samaritans here is some thing I found from Insight on Scriptures Bible encyclopedia. Apparently my assumption that the term Samaritans was used in Bible to refer ten tribe kingdom of north was correct, but only until their conquest in 740 BC. After that the term started to have a different meaning. Assyrians had a practice of removing captives from conquered territory and transplanting in their place peoples from other parts of the empire to avoid future uprisings. So in this instance other national groups brought into northern territory eventually became intermingled both racially and religiously with remaining minority Israelites in north. At some point later the name carried more of a religious rather than racial or political connotation. Samaritans acknowledged only the first five books of the Bible (Pentateuch or Torah) by Moses as authentic. The division is very clear when Samaritans opposed Jews reconstructing their temple and walls of Jerusalem after return from exile in 537 BC. This new religion can be traced back to northern kingdom's first king Jeroboam's efforts to alienate his people from southern kingdom by encouraging calf worship in the name of Jehovah. This is so that he could prevent people from north visiting Jehovah's temple in Jerusalem located in southern kingdom and getting reunited. In time religious and political differences between Jews and Samaritans widened to the point they didn't mingle each other. Jews looked down on Samaritans as having an inferior and polluted form of worship, while Samaritans believed the opposite. Then I had my aha moment.
In a similar line the term Jews was originally applied to those from the tribe of Judah in southern kingdom. After the end of exile in Babylon this included all Israelites joined them in their restoration of worship which came to be known as Judaism. People of the nations who adopted Judaism as circumcised proselytes also identified themselves as Jews. People of the other nations were referred to as Gentiles.
What is more interesting is that Samaritans exist even until today in modern Israel! Like their ancient counterparts modern Samaritans only regard the first five books of Bible from Moses as being authentic. Their version of the first five books is called Samaritan Pentateuch (Samaritan Torah) which is almost identical to first five books of modern Bible translations. In fact it is quite accurate that some modern Bible translations use Samaritan Pentateuch as a comparative reference in their translation work. One peculiar belief of Samaritans is the special importance to Mount Gerizim which they consider as a holy mountain of God. Even today majority Samaritans live nearby this mountain and consider it as holy.
Mount Gerizim is the place near which Jehovah promised Abraham (forefather of Israelites) that he will bless his offspring and give them "this land". Jacob, Abraham's grandson also once camped in its vicinity. Later under Moses instruction in 14th century BC the tribes of Israel assembled at Mount Gerizam and Ebal and the people heard the reading of the blessings they would receive if they obeyed Jehovah and the maledictions that awaited if they disobeyed. Modern archaeologists have confirmed that due to the excellent acoustics in this area even today a large group of people could hear the words from positions in front of either mountains Gerizim or Ebal.
This all makes sense rewinding forward to 1st century CE especially when we compare the account in John 4:7-26 when Jesus was in Samaria. A Samaritan women said to Jesus "Our forefathers worshipped on this mountain, but you people say that in Jerusalem is the place where people must worship". In reply suggesting salvation not just belongs to Jews he said, "the hour is coming, and it is now, when the true worshippers will worship the Father [Jehovah] with spirit and truth, for indeed, the Father [Jehovah] is looking for ones like these to worship him".
The Samaritans also believed in the arrival of a savior just like the Jews. This is because they probably took note of what Moses said about another great prophet who will be raised by God after his death. (Dueteronomy 18:18-19) That's why she replied to Jesus "I know that Messiah is coming, who is called Christ. Whenever that one comes, he will declare all things to us openly." And then Jesus revealed to her "I am he, the one speaking to you". When touching historical facts the internal harmony of Bible is amazing even though it was written over a long period and writers themselves were not contemporaneous.