"Lincoln Memorial" at the end . . . what slaves did the ape free?

The last scene of the movie has given me cause for thought. There is an ape seated in the "Lincoln Memorial" and you can see some writing about "all apes created equal" so . . . what got set free by Ape Lincoln? Sorry about the pun (sorta).

Listed under "Goofs" Someone asked how did the other humans know about "the human who defies apes." Simple, just like my people (red), used smoke signals.