The Jews are only Part of Israel
Only two of the twelve tribes are Jews. After the seventy years of captivity, commenced by Nebuchadnezzar, many Israelites returned to Jerusalem (Nehemiah 7:73). However, this number, 42, 360, was even far less than the number which had come out of Egypt, and comprised predominantly those Jews who had been living in Jerusalem prior to the captivity (Nehemiah 7:6). Thus the return under Cyrus was of some of the Jews and the ten tribes remained in dispersion (ref. Matthew 10:6). So too, the Jews today are descended from only two of the twelve tribes, the other ten still being "lost".