The Message wouldn't have been written if Gill Scott or The Last Poets hadn't plowed the field ahead of time. "The New Sound" had a lot of socially conscious stuff that came before it. Afrika Bambaataa, Kurtis Blow and The Furious Five are all good examples. And surly the whole political consciousness stuff didn't hit it's full blossom until, I'd say, Public Enemy hit the the scene but it was foundational right from the start.
Oh don't get me wrong, I know it was there from the beginning, but it was still largely a "party" scene. Afrika Bambaataa's politically conscious songs were still very party-oriented, and Grandmaster Flash actually wasn't comfortable with The Message being on the album because he considered it too different from the style. The synthesis was definitely there from the beginning, but it really gained prevelance in the early 80's when there was more importance put upon the lyricism. This is part of why I always considered Hip-Hop and Punk to be sibling genres. They didn't arise out of political reasons, but they gravitated to them so easily.