There's a good reason the chimpanzees on Monkey Island, a small piece of land near Liberia, are so murderous. (Did we not mention they were murderous? Because they super are!) They were all dumped there after years of suffering in a research laboratory, where they were constantly stabbed with infectious-disease-filled syringes to advance the knowledge of man. After they were used to create a hepatitis B vaccine and make blood transfusions safer, it was decided that as a small kindness in return for their service, they would be put out to pasture instead of tossed in an ape chipper. And like many retirees, they don't like anyone trespassing on their land. The locals on the mainland are terrified of the place, with one telling a visiting journalist, "They will eat you raw!"
The research facility has long since been shuttered, but the chimps remain (and are reproducing), having now survived not only the diseases they were purposefully riddled with, but also multiple civil wars, an Ebola outbreak, and the occasional reckless tourist. The main danger they now face is starving to death, but a few humans brave the wrath of the righteously homicidal hominids to regularly deliver food, no doubt looking to curry favor for the inevitable Planet Of The Apes situation this is obviously building to.