This is a book I read when I was in high school. The main story revolves around these ape-like humanoids, who are the main characters, that get invaded by humans and later enslaved. It was a softcover book and the cover had these ape-like human hybrids hiding by a big tree from the invading humans.
I am not sure about whether they can use magic or not, but it's more or less how the main characters overcome the invasion. Later on, some of the humans realize what they are doing is bad and join forces with the ape-like humanoids.