The film takes place 10 years after the events of Rise of the Planet of the Apes, in which scientist Will Rodman (James Franco) genetically alters chimpanzees while trying to find a cure for Alzheimer's disease.
Rodman's testing affects test subject Caesar, who gains intelligence and leads an uprising of the apes which ultimately leads to Charlton Heston landing his space ship on an unknown planet that *SPOILER ALERT* turns out to be Earth, where apes have become more intelligent than humans and are the dominant species. And like leather jackets.
After Caesar's uprising, humans spent the better part of the following decade fighting a devastating virus and each other, and now the apes are ready to take over as the most intelligent beings on the planet.
"We've been through hell together," Dreyfus (Oldman) says. "We spent four years, four years, fighting that virus, and then another four fighting each other. It was chaos. But you all know what we're up against."