Well, try I'M A GOOD OLD REBEL, a protest song from the 1860's. Or search for "Joe Hill" in the Forum. Lots of union songs beginning in the 1890's and running through the 1940's. Pete Seeger and Woody Guthrie, Butch Hawes et al., the Almanac Singers, used to sing those. Then there are all those Jacobite songs.
But as for "Johnny, I Hardly Knew Ye," there is a thread on that, and it appears that an older song was transformed into a Song of Protest in the 1960's, by adding a final verse that changed its meaning.