Good question and I should have a better answer. My memory at the moment is the "Cohens" are the oldest Jewish bloodline. Jews lived around the current State of Israel, though not sure the exactly where or when. When the Romans rose to power Israel, like other people subjugated by the Romans, handled it in a complex manner. The gist of it is that Rome essentially stopped Israel from governing its own affairs because it wasn't respectful enough (I believe history may repeat there). At some points a tribe of Jews moved to Ethiopia. I'm sure there are many books an articles on this subject. Even back then, the Jews were comprised of many clans.

Today there are basically Ashkenazi and Sephardic Jews. My DNA test says the former.