But we didn't have natural echo chambers of that sort and magnitude, because we didn't live in a global village.

I believe that the ideological self-segregation is mostly because you can choose who to interact with. That's also why it's primarily online, because you cannot choose to a similar degree offline, and the physical distance between you and your near-duplicates is too large for echo chambers to form, unless you make an intentional move to bring them together (e.g. sects moving to a certain location).