H. G. Wells was both the author of the original source -- an essay, rather than an actual novel, concerning mankind's future -- and the screenplay (in conjunction with Lajos Biro) of this epic science fiction tale, but it was producer Alexander Korda who framed the terms on which it is presented, vast and elegant, and visually striking. Opening in the year 1940, we see the next century of human history unfold, initially with amazing prescience. In Everytown (a stand-in for London) in 1940, the people prepare to celebrate Christmas amid rumors and rumblings of war -- forward-thinking pacifists like John Cabal (Raymond Massey) try to raise concerns amid a populace either too fearful to think about the risks, or so pleased with business conditions that they're oblivious to the downside of war. And then it comes, devastating Everytown (in scenes shockingly close to the actual World War II London blitz, a half-decade away when these scenes were written) and the country, and finally the world. After 30 years, the war goes on, except that there are no more nations to fight it, only isolated petty fiefdoms ruled by brigand-like strongmen, running gangs organized like tiny armies. Among the most ruthless and successful of them is Rudolph (Ralph Richardson), who runs what's left of Everytown. He keeps his people in line by force, and his war with his neighbors going with his bedraggled troops, while pressuring the tiny handful of scientists, mechanics, and pilots to keep as many of the aging, decrepit planes as they can operating. A few educated men around him -- whom he doesn't really trust -- try to resist the worst of his plans and orders, while going through the motions of carrying them out.
And then, one day, out of the sky comes a plane the like of which they've never seen before, sleek and fast, and piloted by a mysterious man whom Rudolph orders imprisoned. It is John Cabal, older but just as dedicated to the cause of peace, and ready to fight for it. He announces the existence of a new order, run by a society of engineers and scientists, called Wings Over The World, here to re-establish civilization. Rudolph will hear none of it, thinking instead to use Cabal's plane and those of any of his friends who follow as weapons of war -- but Rudolph's wife Roxana (Marguerite Scott) sees the wisdom of what Cabal offers and helps him. The bombers of Wings Over The World drop the Gas of Peace, which puts the entire population of Everytown to sleep -- all except Rudolph, who goes down fighting and dies -- allowing the army of the Airmen to enter and free the city.
Seventy years go by, during which the Earth is transformed and a new civilization rises, led by scientists and engineers. Immense towers now rise into the sky, and the population is freed from most of the concerns that ever led to it war. In fact, a new complacency starts to take hold amid a populace for whom most needs are now easily met -- all except the leaders, engineers who keep advancing, year after year, with new projects and goals. And now, having conquered the Earth and all of the challenges it has to offer, Oswald Cabal (Raymond Massey), the great-grandson of John and the current leader, is about to embark on the grandest project of all, moving into deep space. The first launch of a manned vehicle, fired by the Space Gun, is about to take place. But there is discontent being spread by the sculptor Theotocopulos (Cedric Hardwicke), who is weary and distressed from this constant push toward new advances and progress -- he wants mankind to reassert itself over this ever-advancing technology, and sees the Space Gun and all it represents as a new threat. In a speech, he exhorts the restive populace to stop the launch. They proceed, en masse, to attack the Space Gun, while Cabal struggles to beat them to their objective and take the next bold step into space. "All of the Universe," he declares, "or nothing -- which shall it be?"