If Quentin Tarantino ever makes the Star Trek movie he keeps yammering about, it’ll get mischaracterized as his first foray into science fiction. Yet the truth is that at least two of his four recent movies are best understood as examples of a special subgenre of science fiction, the alternative history. These are all films that seem like they are set in the past (World War II, 1969 Hollywood) but make sense only when we realize they take place in parallel universes where history diverges radically from the actual past.

Inglourious Basterds ends with a ragtag Jewish militia, under the leadership of Lt. Aldo Raine (Brad Pitt), bringing World War II to a satisfying end by assassinating the Nazi elite, including Adolf Hitler and Joseph Goebbels, at a movie screening. For good measure, Raine and his henchmen carve a swastika in the head of an odious Nazi “Jew hunter” who had switched sides in the last minute in the hopes of being rewarded by the Americans. This is, of course, wildly at variance with reality. The Nazi leadership class was decapitated by the Red Army. While some Nazi war criminals were punished, all too many escaped unscathed, especially since more than a few were recruited by the victorious powers, who wanted their services as military strategists, spies, and weapon makers for the Cold War.

Tarantino’s latest film, Once Upon a Time in Hollywood, works on a smaller canvas but with a similarly audacious ending, with Brad Pitt once again being recruited to radically alter well-known history. In the movie, the infamous night when members of Charles Manson’s cult killed actress Sharon Tate and four others is given an unexpectedly cheerful denouement. The killers are thwarted by a fictional duo, cowboy actor Rick Dalton (Leonardo DiCaprio) and his stunt-double-turned-factotum Cliff Booth (Brad Pitt).

It’s easy to chalk up Tarantino’s playing with history as yet more proof that he’s an irresponsible nihilist, someone who crafts narratives simply for their shock value, with no sense of loyalty to canons of accuracy and verisimilitude. Film critic Jonathan Rosenbaum described Inglourious Basterds as “akin to Holocaust denial.” He added that “Inglourious Basterds makes the Holocaust harder, not easier to grasp as a historical reality. Insofar as it becomes a movie convention—by which I mean a reality derived only from other movies—it loses its historical reality.”

By the same token, Once Upon a Time in Hollywood can be seen as insulting to the memory of the various real figures, such as Sharon Tate or Bruce Lee, whose life stories are distorted in the film. (Lee’s family has complained about his being portrayed as a belligerent boastful loudmouth who easily gets bested in a fight with Cliff Booth.)

These accusations can be partly answered by noting that Tarantino isn’t giving history but alternative history. One of the key functions of alternative history as a genre is to offer a sly commentary on real history. A famous example is Philip K. Dick’s The Man in the High Castle (1962), where the Axis powers win World War II. In the novel, the victorious Nazis and Japanese imperialists divide the world between them and carry out an arms race that threatens human survival. The novel was obviously alluding to the actual Cold War, recasting it in grotesque terms as a battle between competing fascisms, to call attention to its absurdity.

In a like manner, Tarantino’s imaginary history is meant to cast a critical eye on actual history. The easy putdown of Tarantino is that he’s offering gleeful revenge fantasies by creating scenarios where violence can be inflicted on easy-to-hate bad guys (Nazis, the Manson family, or, in Django Unchained, slave owners).

Yet the thrill of righteous vengeance acquires a melancholy taste when we realize that the stories we are seeing didn’t happen. The discrepancy between what should’ve happened and what we know happened calls attention to how inadequate the real world is. At the end of Once Upon a Time in Hollywood, you don’t feel any happier that the fictional Sharon Tate survives. Rather, you feel even more acutely the loss of the real Tate.

Both celebrants and naysayers of Once Upon a Time in Hollywood make a mistake in treating its seeming nostalgia at face value. Richard Brody of The New Yorker didn’t like the film, seeing it as a regressive reverie about “a world in which the characters, with Tarantino’s help, fabricate the sublime illusions that embody their virtues and redeem their failings—and then perform acts of real-life heroism to justify them again.”

Caitlin Flanagan of The Atlantic loved the movie as much as Brody hated it, but she shares his view that it celebrates old-time Hollywood values. For Flanagan, it’s “a major motion picture in 2019 about a man with a code, a man who hews to the old values of the Western hero.”

If we see the film as uncritically nostalgic, then it really is nothing more than a white-male revenge fantasy about two downwardly mobile dude-bros who swat down threats from various insurgent groups (people of color, nagging wives, and hippies). But this is a one-dimensional view of a complex and self-searching movie.

Where Brody and Flanagan both go wrong is in overestimating how celebratory the movie is of its two heroes, and especially Cliff Booth. (My Nation colleague Stuart Klawans is much closer to the mark in calling attention to the way the film is an exercise in self-criticism on Tarantino’s part.)

As played by Brad Pitt, Booth of course has a lean, laconic charisma. Yet he’s also a man of violence. Other characters in the movie talk about rumors that he killed his wife, a murder that seems all too plausible. His two-fisted interactions with Bruce Lee and hippies are implicitly contrasted to the happy-go-lucky acceptance of Sharon Tate (who takes Lee as a mentor and embraces a hippie hitchhiker she gives a ride to).

It’s true that Booth (along with his buddy Rick Dalton) earns redemption by fighting off the Manson cult. But the fact that this never happened in reality (something that the audience is all too aware of) makes this a bittersweet triumph. Just as Inglourious Basterds underscored how the actual World War II didn’t have the satisfying slam-bang climax of a war movie, Once Upon a Time in Hollywood reminds us that action-star heroics existed only on the big screen in 1969.

The title should be a clue. It’s an allusion, of course, to the films of Sergio Leone (Once Upon a Time in the West, Once Upon a Time in America). But it’s also a reference to fairy tales, to make-believe stories that we use to comfort children. Tarantino is playing a double game with his alternative histories: offering us the exhilaration of a tried-and-true Hollywood ending, but also reminding us that such happy outcomes happen only in the movies.