Earlier quoted context omitted.
"(also, categorizing propaganda posters as art, ewwh...)" Heinrich Heine, the german Poet declined working for the socialist party despite symphatising saying something like: I want to remain a poet, you want a propagandist. A poet cannot be a propagandist at the same time.
Art for much of human history was devotional, a lot of our greatest artworks today are still religious in nature. The idea that art solely is an act of rebellion rather than say worship, is a pretty modern idea that has produced some rather questionable art by the way. Of course a great artist or poet can be a propagandist. Riefenstahl, Mann, a lot of German nationalists were great artists. One of the most famous wor…
I'd be open to discussion where the exact limit is. Lenin died in the 1920s, Marx even earlier, but those two were frequently depicted in Communist propaganda of the 1980s.
So it is probably "hundreds of years".