I agree with GUEST, Shimrod. A song has to go through a certain process in society, aging, changing, and otherwise maturing until it has reached a point that it's subject is historical not current. Many songs mentioned here up through the WWI era I think could now be considered folk songs IF they came into being in the era they describe. Recently penned lyrics about old events, historical or otherwise, are not folk though they may be folk-style songs (acoustic instrumentation generally). Songs after about WWI, whether written for $ or not, whether overtly political or not, in my view aren't really folk songs yet. And certainly the protest songs of the 60s forward, whether protesting militarism, political events, or social trends, have not yet become "folk".

SC