All of the "successful" subs are either small enough to self-govern effectively because they feel like actual communities or they have hardcore, uncompromising moderator teams that enforce the rules swiftly.

askhistorians is the best example I can think of. askscience close behind.

r/history is heavily moderated, and primarily political positions need to be backed up with actual historical facts and discussion (and not out-of-context common talking points) or it'll be called for what it is and deleted.