What is it with ape movies and the Vietnam War? “Kong: Skull Island,” which came out in March, and this week’s new release “War for the Planet of the Apes” both echo that yearslong conflict and, very specifically, Francis Ford Coppola’s 1979 epic, “Apocalypse Now.” What’s the connection? And don’t say “guerrilla” warfare.

It may have to do with the horror and dehumanization with which Vietnam War remains synonymous. “War for the Planet of the Apes,” the final episode in a trilogy that began in 2011, envisions an all-or-nothing battle between increasingly intelligent apes and steadily devolving humans. With its themes of survival and extinction — plus a chilling reminder that Mother Nature looms largest of all — “War” is a summer blockbuster that packs an existential punch.

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“War” features another star turn from motion-performer Andy Serkis as the alpha-simian Caesar, whose fellow apes are living in the woods and avoiding troops of armed humans. Caesar, a stern but peaceable chieftain, meets his mirror-image in the Colonel (Woody Harrelson), who leads a murderous militia-cum-cult bent on eradicating all apes (known in military parlance as “kong”). Joining Caesar on his mission to end the war are the gentle orangutan Maurice (movingly played by Karin Konoval), a zoo refugee nicknamed Bad Ape (an enjoyable Steve Zahn) and, by happenstance, a little human girl (Amiah Miller) whose mysterious lack of speech suggests a species in trouble.

This is a major improvement over the overwrought previous film, “Dawn of the Planet of the Apes.” The subtitles that translate the apes’ sign language still tend to dull the dialogue but, by contrast, Harrelson’s live-wire Colonel chews up the scenery. He’s clearly modeled on Marlon Brando’s Colonel Kurtz from that famous Coppola film: bald, lisping, clearly insane and given to morbid speeches about savagery and beauty.

In its pulpy way, “War for the Planet of the Apes” — vigorously directed by Matt Reeves from Mark Bomback’s screenplay — captures the zeitgeist. It presents a civilization gripped by fear, divided by hatred and hurtling toward utter, slate-wiping destruction. If this shiver-inducing piece of entertainment has a message, it’s the one spray-painted within the Colonel’s fortress: “Ape-pocalypse Now!”