What happened to Earth in the 1968 Planet of the Apes?

Question

The ending in Boule's Book is different and I think the ending of the film is one of the great masterpieces of the adaptation.

But whats supposed to happen in the film's Earth? What lead to the rise of the apes?

Answer 1

In 1968, "YOU MANIACS! YOU BLEW IT UP! AH, DAMN YOU! GOD DAMN YOU ALL TO HELL!!" meant nuclear war. We were still doing duck and cover back then.

Answer 2

tl;dr - The supposed fate of the Earth, and the path of its fate, changes slightly in each film, but there's no nuclear war explicitly shown.

At the end of the first film (Planet of the Apes), the only thing we know for sure is that Man fell and Apes rose. While there was presumed to be a great war, there's no definitive proof of that. The dilapidated state of the Statue of Liberty, and of New York City in the second film could easily be explained only by hundreds of years of being allowed to "go to seed".

In the second film (Return to PotA), we learn about a group of humans, horribly mutated by the leaking radiation from a powerful nuclear missile they protect and worship. It explodes at the end of the film, seemingly a definitive end to the series, but when there's money to be made, all things are possible.

In the third film (Escape from PotA), Cornelius and Zira (from the first film) and a third ape figure out how to raise, repair, fuel and launch Talyor's ship from the first film, and travel back through the same time warp to our present. Here, we get a bit more information about the Earth's future - Zira explains that according to their history (which never seems to get mentioned at all in the first film, but we'll ignore that), Man was the dominant species, but began to train apes to perform menial tasks. And one ape became advanced enough to refuse an order, and say "no". That was the beginning of the rose of Apekind.

In the fourth film (Conquest for PotA), we see those events come largely to pass. With the humans assuming they had avoided their future fate by destroying Cornelius, Zira, and their child, they didn't worry about the predicted events coming to pass - a plague destroying cats and dogs, and humanity choosing to train apes as pets and, effectively, slaves. The ape child, Caesar, had not died, and secretly begun an underground movement to organize the apes, and begin the titular Conquest.

The final film of the series (Battle for PotA) takes place a number of years after Conquest, with Apes in charge of things. Some Humans are assisting them, some are fighting against them. We see the birth of the nuclear mutant group, and we see the change in the relationship between humans and apes sour.

There's a LOT of time unaccounted for - millennia, really. Plenty of time for men to "devolve" into non-verbal hunter-gatherers, and for the cities to become vine-covered wastelands. There's plenty of "Yeah, but..." questions and plot holes in the films, but all told, it's a solid series that speaks to humanity's believe that it can escape its fate.