Blues came from american folk and they share very similar structure. I think that constitutes as a sub-genre. Country also came from american folk and shares similar structure.

Blues can be just as traditional as folk. And folk can be just as personal and improvisational as blues (funny you mention Woody Guthrie, Pete Seeger said that Woody could pick up a guitar play the longest cowboy ballad you ever heard and you'd never hear it again). I don't see either as distinguishing traits. Blues as we know it has taken its notes from american folk. Who's a pre-late 1800's blues artist?

who deleted all of their posts?

I think blues had its roots in African American tradition rather than American roots music.