The Prime Directive: According to Star Trek canon, it's the guiding principle of the United Federation of Planets and prohibits Starfleet personnel from interfering with the natural internal development of alien civilizations. First introduced about two-thirds of the way through the first season of the original series, the Prime Directive has cropped up in four of the five Trek series to date, with varying degrees of importance and success.
The problem with the Prime Directive is that while it prevents Starfleet or Federation personnel from interfering with other societies -- or worse, imposing its own values on them -- it also acts as a storytelling inhibitor. What is Captain Kirk supposed to do when he beams down to a planet where the local version of the Third Reich is about to launch its own Final Solution on another race of people -- just stand there? The way Star Trek was set up, the show almost forced Kirk repeatedly into situations where he had to violate the Directive, and he did so. Otherwise we'd be staring at a blank screen for most of that hour.
Here are 11 times that Kirk intervened in a society on another planet and violated the Prime Directive, along with one time that he played by the rules. Was he right or wrong?
1. "The Return of the Archons"
The very first mention of the Prime Directive was in this episode, in which Kirk and the Enterprise crew encounter a society that has been stagnant for thousands of years. All expression and creativity are repressed except for an event called the Festival, in which pent-up emotions of all kinds are released in a frenzy of violence and sex (kind of like an EDM event). This scenario was created millennia ago by a long-dead man named Landru, who programmed a supercomputer to keep things running after he was gone. Kirk and his landing party must prevent themselves from being "absorbed," but Kirk also decides that the computer must go and the society allowed in some way to begin evolving again.
End result: Landru is destroyed and the Betans are left somewhat rudderless, although Kirk promises to send educators to make them into good little Federation citizens.
2. "A Taste of Armageddon"
The people of Eminiar VII and Vendikar have been at war for centuries, but it's all simulated -- all except the casualties, that is. Computers on both sides map out simulated attacks and inhabitants pegged as casualties report to disintegration chambers to die. With neither civilization seeing the true horror and destructiveness of war anymore, they have no reason to end it. A landing party led by Kirk are tagged as collateral damage, but you know Kirk isn't walking into some booth to disappear. So he decides to intervene and destroy the computers that run the war.
End result: Faced with the threat of real war and the total destruction of both planets, both sides decide to start talking...with a Federation ambassador conveniently on-site.
3. "The Apple"
In addition to being one hell of a silly episode, "The Apple" offers up one of Kirk's worst defenses of violating the Prime Directive. Yes, the primitive society that the Enterprise encounters on the planet Gamma Trianguli VI has lived pretty much the same way for 10,000 years under the auspices of self-aware machine/reptilian stone god Vaal, but who the hell is Kirk to decide that they must change things up? He takes it upon himself to destroy Vaal, saying he'll take his chances with the Feds over violating the Directive.
End result: The "feeders of Vaal" are left in chaos by the destruction of the machine, but Kirk reckons they'll be all right. How nice of him.
4. "Friday's Child"
This one involves a relatively minor violation of the Directive, with Kirk, Spock and McCoy getting involved in tribal politics on Capella IV. Specifically, they escape being held prisoner by the Ten Tribes (who are also negotiating with the Klingons for the same mining privileges that the Federation wants) and take the pregnant widow of the tribal leader with them -- a woman who was fully prepared to die along with her unborn child. It's a small alteration in the course of events on the planet, and Kirk doesn't think twice about it, since he's both saving a woman and a kid and working toward securing those mining rights for the Federation.
End Result: The woman, Eleen, has her baby, the Klingon rep gets killed and the new leader of the Ten Tribes is impressed enough with Kirk to give the Federation the mining exclusive. A win-win for everyone.
5. "A Piece of the Action"
This was the first of a handful of episodes in which the Prime Directive has already been broken and Kirk has to sort of break it again to restore things to normal. In this case, the people of Sigma Iotia II, a highly imitative culture, have been corrupted by a book on the Chicago mobs of the 1920s that was left behind by an Earth spaceship 100 years earlier, before the Prime Directive existed. When the Enterprise gets there, the entire planet is divided and run by gangsters, forcing Kirk to put on his best mob boss accent and make them all an offer they can't refuse (basically he points the Enterprise's phasers at them).
End result: Since this episode was a comedy, everything's very light-hearted -- but basically Kirk puts the Federation in charge of the planet to move it away from gangland culture.
6. "A Private Little War"
This episode was meant to be an allegory about the then-raging Vietnam War, with the Klingons and Federation standing in for the Communist bloc and the U.S. and its allies respectively. The Enterprise visits a planet called Neural, where the inhabitants are gentle, peaceful and primitive; but when they get there they discover that one of the planet's tribes has flintlock rifles -- an almost impossible feat for this civilization at this point in time. It soon becomes apparent that the Klingons are arming one side with the goal of taking over the planet by proxy, so Kirk must decide whether to break the Prime Directive and arm the other side to maintain a balance of power.
End result: Kirk arms the tribe led by his friend Tyree, but takes no joy in doing so, since he knows all too well where this can lead. Kirk's solution in this particular episode is not an easy one.
7. "Patterns of Force"
When the Enterprise journeys to the planet Ekos to find out what happened to Federation cultural observer John Gill, Kirk and Spock discover to their horror that Ekos has adapted the fascist ideology and symbols of the Third Reich. The Nazi regime -- of which Gill is apparently the Fuhrer -- plans to wipe out anyone from the neighboring planet of Zeon who is now living on Ekos before destroying Zeon itself. With the Prime Directive already broken, Kirk must find out what went wrong and why Gill seemingly decided that transforming the planet into a Nazi nightmare was a good idea.
End result: It turns out that Gill utilized certain aspects of Nazism to get the barbaric Ekosians under control, until he was drugged and betrayed by an underling who is much more Hitler-like in his tactics. Both men die, but not before Kirk manages to revive Gill and make him give a speech renouncing the entire situation. It's implied that the two planets will work things out on their own.
8. "The Omega Glory"
Kirk and Spock must contend with a Starfleet captain gone rogue, a deadly disease that turns people into leftover piles of salt from "The Man Trap" and the primitive remnants of a civilization that somehow paralleled ours, right down to the conflict between the U.S. and the Soviet Union -- except that their Cold War turned hot and decimated the place. This extravagantly weird episode -- one of the first scripts Gene Roddenberry ever wrote for Star Trek, oddly enough -- finds Kirk having to fix a broken Prime Directive again, this time with a bunch of fistfights and flag-waving nonsense.
End result: Kirk reads the Pledge of Allegiance and the Constitution at everybody, which has the magical effect of establishing peace between the Kohms and Yangs -- something we've still never quite achieved here in 70 years of wars cold and hot.
9. "Bread and Circuses"
Kirk, Spock and McCoy are trapped on a planet that mirrors the Roman Empire, except with modern technology, where they are forced to fight in televised gladiatorial contests. This is the only Star Trek episode to feature a shared writing credit by Gene Roddenberry and producer Gene L. Coon (the "other" Gene who was a fundamental part of many of Trek's most successful episodes), so you would think that these guys would get the whole Prime Directive thing right. And they actually do: Kirk and Spock do not interfere with the evolution of this strange culture, and even the by-now-standard rogue starship captain gets dispatched by a knife in the back before he can do any more damage.
End result: Kirk, Spock and McCoy manage to escape without interfering in the society, which means that the high-tech Roman Empire will carry on at least for a while. In other words, without breaking the Prime Directive it was like they were never there.
10. "The Paradise Syndrome"
Kirk loses his memory on a primitive planet and awakens to find himself treated like a god by the local inhabitants, who strongly resemble Native Americans. Meanwhile, with Kirk seemingly missing, the Enterprise must find a way to deflect an asteroid headed for that very same planet. The answer may be inside the mysterious obelisk that wiped Kirk's mind in the first place. Probably the most benign violation of the Prime Directive ever, this merely involves Kirk and Spock finding a way back inside the obelisk so that they can turn on the mechanism left behind by an ancient race for the specific purpose of deflecting asteroids (how convenient!). Spock and McCoy are also seen beaming down by the villagers, a no-no if you want to keep yourself Directive-pure.
End result: The asteroid is deflected, although Kirk loses the village girl he fell for and was about to have a child with. At least the planet is saved, though.
11. "For the World is Hollow and I Have Touched the Sky"
This time it's a generation ship disguised as an asteroid that's on a collision course with a heavily populated planet, and it's McCoy's turn to fall in love since he's dying of a rare disease and decides there's no better way to live out what's left of his life than on an alien ship with a woman he met five minutes ago. The computer that controls the ship doesn't like Kirk and Spock snooping around to find the steering wheel and zaps them, but McCoy eventually finds the sacred knowledge which is inexplicably kept hidden from the people it's meant to save. Strangely similar to "The Paradise Syndrome," this is also a light violation of the Prime Directive since if the Enterprise boys don't interfere, the Yonada will smash into someone else's planet.
End result: The Yonada gets a course correction and there's even a cure for McCoy's illness in their archives, leading to the fastest divorce in space history as he bids goodbye to the ship's high prietess just before the credits roll.
12. "The Cloud Minders"
On the planet Ardana, the wealthy and sophisticated elite live in the floating city of Stratos while the laborers (Troglytes) who work the mines on the ground have to tough it out on the planet's rough surface. Rebels are sabotaging the delivery of a rare mineral called zenite to the Enterprise, which makes Kirk so cranky that he decides to stick his nose in Ardana's slowly accelerating civil war. A very thinly-disguised tale of haves and have-nots, "The Cloud Minders" takes a bit of an easy way out when it's discovered that an invisible gas in the mines, and not neglect and abuse from the cloud-dwellers, has turned the miners into near-savages. Kirk gets a whiff of the gas himself, which is perhaps why he decides to intervene with such hammy abandon.
End result: Kirk forces the Ardana leader Plasus to dig in the mines himself and enjoy the effects of the gas, making Plasus realize that maybe they've been hard on the Troglytes after all. Kirk gets his shipment, the Troglytes get gas masks, and it's implied that they might be allowed into Stratos' restaurants at some point soon.