There is no rule, no law, that is more Federation and Starfleet than the Prime Directive. It is one of the cornerstones. It's also known as General Order Number One; "No starship may interfere with the normal development of any alien life or society."

The Prime Directive is not just a set of rules; it is a philosophy… and a very correct one. History has proven again and again that whenever mankind interferes with a less developed civilization, no matter how well-intentioned that interference may be, the results are invariably disastrous."

It's a straightforward concept before a civilization achieves warp speeds, they must be allowed the natural progression towards that. Even in the face of destruction, if that's how the dice rolls for your civilization, then that will of the universe will be respected. 

The very core of the philosophy was the concept that Starfleet should refrain from any interference, covert or otherwise, even if well-intentioned.

So fundamental was the observance of the Prime Directive that Starfleet officers would uphold it, even if it meant their lives.

The origins of the Prime Directive are Vulcan.  When or how they came up with this rule for themselves is unknown, but T'Pol of the Enterprise advised Captain Archer of it. He strongly agreed with the philosophy after seeing the damage done by interference on a pre-warp planet.

It wasn't just the General Order, the Prime Directive had 47 sub-orders by the end of the 24th Century.

Some of them included:

• Providing intelligence of the greater universe, (the Federation's or any other alien species) even if that species leaders already know of it, to pre-warp societies
• Avoiding or subverting the established laws of a society.
• Helping to escape a natural disaster known to the civilization, even if Starfleet's inaction would result in a society's end
• Helping advance technologies or science of pre-warp societies
• Advancing the overall development of a pre-warp society

The Prime Directive on first read seems simple and straight-forward. But nothing is ever purely logical. It has been bent, broken, or abandoned in the course of the Star Trek universes. Here are a few examples of it being tested.

Trouble with Kirk

Captain Kirk had trouble following the Prime Directive on numerous occasions.

When the Enterprise dealt with the people of Beta III, they discovered a stagnant, pre-warp civilization. Rather than abiding by the Prime Directive, Kirk dismantled the ruling supercomputer Landru, which freed the people but left their society in need of further direct intervention as seen on Lower Decks when the Betans attempt to turn it back on.

In another instance, Kirk destroys the Vaal, a reptilian machine that has kept a society primitive for over 10,000 years requiring the Federation to come in and pick up the pieces.

In another mission, on the planet Neural, Klingons have decided to give advanced weapons (flintlock rifles) to one faction of the population, to take over the planet by proxy. Kirk decides to balance the scales, violating the Prime Directive and arms the other faction, believing that was the lesser damage.

The cowboy captaining of Kirk reflects the times in which the show was made. Kirk doesn't have to be there to pick up the pieces of the newly freed, he is off to the next mission. The conflict between acting on conscience to free people that you believe need your help, or to leave them be, reflected the times as Star Trek ran during the Vietnam War. The Prime Directive is a policy of noninterference.

That's why there's such a sharp contrast between Kirk and Picard. They are opposites, especially regarding the Prime Directive.

It's the principle…

The USS Enterprise under Captain Jean-Luc Picard became a place of ideals and the expectation of always presenting the very best of Starfleet. Even when he did violate the Prime Directive, it was only to limited degrees or to save what had become a very messy situation.

When Data was contacted by Sarjenka of Drema IV, this contact ultimately gave Picard the excuse to save her and her people without them knowing as her communication was a direct plea for help. Otherwise, he would have allowed her and the rest of her people to die per the Prime Directive.

When the power source keeping a research location hidden from a proto-Vulcan civilization fails, killing some of the staff, the Enterprise goes to assist them. Dr. Crusher breaks the Prime Directive by beaming and treating one of the locals who is hurt investigating the observation post. This leads to a situation where he tells the populace of "The Picard" rekindling belief in the supernatural. It takes a full intervention by Picard to stop this belief.

 When Wesley Crusher was going to be executed for his crime of falling into some flowers by the Edo people, Picard intervenes asking "When has justice ever been as simple as a rulebook?" Picard's duty to protect the crew or their children, even when it endangered thousands, outweighed the dictates of the Prime Directive for Picard.

The long way home

Captain Janeway of the USS Voyager had the choice between leaving the Caretaker's Array or destroying it as the Caretaker died he. Lt. Tuvok advised Captain Janeway of the potential Prime Directive violation of involving Voyager in the struggles of the Kazon and Ocampa. Destroying the array "would affect the balance of power in this system. The Prime Directive would seem to apply." However, because the Kazon ship would not have collided with the array if not for the arrival of Voyager and the Marquis ship Val Jean, Janeway's destruction of the array was a corrective action that reinstated the Caretaker's self-destruct plan and thus did not technically violate the Prime Directive. Destroying the array sacrificed returning Voyager to the Alpha Quadrant quickly, leaving them to have to find another slower way home.

The Pralor Automated Personnel Units (APU) were seeking to stave off their extinction with the help of Lt. Torres. Janeway forbade Torres to do this as it was a violation of the Prime Directive. She said it was the "equivalent of altering their genetic structure," and that "extinction is often the natural end of evolution". The APUs kidnapped Torres but she destroyed her work thus removing any interference in their evolution.

Omega

There is one directive that supersedes all others and that is the Omega Directive.

A team of 127 top-Federation scientists, led by the Starfleet physicist Ketteract, was working on a top-secret experiment at a classified research station in the Lantaru sector in the mid-23rd century. Research showed that a single molecule of Omega contained the same power as a warp core. Theoretically this power could sustain a civilization indefinitely. Ketteract's goal was an inexhaustible power source, or as pointed out by Seven of Nine a power that could also be used as a dreadful weapon.  The Borg had been aware of this molecule and had named it Particle 010. Federation cosmologists theorized that the Omega molecule once existed in nature for an infinitesimal period as the big bang occurred. Some even claiming that the Omega was the primal source of energy for the Big Bang.

 The scientists were able to synthesize a single Omega molecule, which only remained stable for a fraction of a second. With destabilization, the research center was destroyed killing all. Discovered during the rescue and recovery attempts was a rupture of subspace within a radius of several light-years, causing warp travel to become permanently disabled.

After this incident, Captain Kirk created the directive and suppressed all knowledge of the events. Only starship captains and flag officers are briefed about it and specialized teams would be dispatched to deal with any Omega-related crises.

Great Bird, great vision

Gene Roddenberry was a World War II Army fighter jet pilot. After the war, he became a police officer with the Los Angeles Police Department. He served in law enforcement for years and then switched to become a writer. In 1963, he helmed a TV show called The Lieutenant, and it featured many as-yet-unknown actors, including Leonard Nimoy.

In the 1950s and 1960s, as the world worked to reclaim itself post-war, the bigger countries preyed on the weaker, less developed ones. It was Capitalism vs Communism. Roddenberry saw this and it is reflected in the future he wanted. Where neither capitalism nor communism wins but a society of free people seeking to better themselves and the universe. The Prime Directive is that continued reflection, giving people a chance to develop how they naturally will without the involvement of 3rd parties like the US or USSR.

It's a utopian dream to be sure, but that's why we watch, especially now with Discovery, where the past will heal the future, bringing back the Federation and its ideals, including the Prime Directive, to protect civilizations that need that shield 930 years from their home.