John 4:9 (NASB)
"Therefore the Samaritan woman *said to Him, “How is it that You, being a Jew, ask me for a drink since I am a Samaritan woman?” (For Jews have no dealings with Samaritans.)
We have many years of history and many explanations for this. The northern kingdom was taken captive to Assyria approx.160 years before Judah, the southern kingdom was taken captive to Babylon. See II Kings 23: 26-27.
God caused all of this to happen: Babylon had taken Assyria so by the time the 70 year captivity was coming to an end, all of God's people in what was Assyria and Babylon were given the chance by Darius to return to Jerusalem to build the second temple to their God.
About 10% went back to rebuild the second temple.
When Samaritans(the people who had not been taken to Babylon and had married non Jews) wanted to help rebuild the second temple were told they were not good enough to join the returning people to rebuild. This is what started the split that grew into such hatred that the non-Samaritans would not pass through Samaria. This hatred went on for 400 +/-years until Jesus did NOT go around Samaria (John 4:4), he needed to go through Samaria; He wanted to end this hatred!
Jesus came to save ALL who would believe on Him. Study the bible to know the truth. Do not believe everything that man has written about the bible. There is much being preached in American churches today that is of men and not of God. Remember that the books of the Bible are not arranged in chronological order. Some chapters of some books are even not chronological. Jesus said that until John the people had the profits and the law; but now all things are given unto Him.