You need to decide whether you're going to go for the broad picture, and give a taste of the songs of diffeent eras and different struggles; or focus on some particular period, and the different struggles going on at that time; or one particular struggle over the generations etc.

In one hour I'd have thought focussing it in some way might be more realistic - for example, it was Civil Rights, you could have abolitionist songs in, as well as more recent ones.

I'd recommend getting hold of Pete Seeger's "Carry it On", if you can, especially for the older songs (and their context), and more recent ones that aren't part of the music industry.