Folk songs came from everywhere,some were composed by every day people,
some by scholars,some by political activists,name a source and somewhere exists a song that originated there.
The thing that unites the songs is they have some quality that touches people in some way.
That quality be it sentiment,tune,national pride or whatever is the thing which encourages singers to learn and sing the song and others to learn it themselves.
The songs have travelled through time largly by oral transmission and have been shaped a little by each of the singers who have transmitted them.
The songs of today if they travel in a similar way could well be considered a folk song in 50 or 100 years time.