“War for the Planet of the Apes” is a film that unapologetically embraces the first word of its title. It opens with soldiers in a lush green forest with nicknames on their helmets, marching toward the enemy through the brush in a style that reminded me of “Platoon.” Over the next two hours, other war films will flash through your mind, most commonly “Apocalypse Now,” which Matt Reeves’ excellent blockbuster cribs from openly, even turning its villain into a Colonel Kurtz in the heart of darkness, complete with shaved head and rambling philosophy. (At one point, graffiti even reads “Ape-pocalypse Now,” as if to make clear that Reeves and company aren’t stealing as much as directly paying homage.) So why turn a franchise about sentient apes into a war movie that echoes the stories of Vietnam? What can be gained from looking at the darkest side of humanity.