Ban on synthetics
The ban on synthetics, also called the ban on synthetic lifeforms or simply synth ban, was a galactic treaty banning all practical research, development, and creation of synthetic lifeforms throughout the United Federation of Planets. The policy was put in place in 2385 after the Attack on Mars and was repealed fourteen years later, in late 2399 or early 2400.

Origin
Several centuries before the 24th century, a group of Romulans detected a message left behind on the planet Aia by an extra-galactic alliance of synthetic life. The message took the form of a vision, informing any synthetic being that might find it about the existence of the alliance and a way to contact them. The vision postulated that the organic creators of artificial beings would inevitably grow envious of their creations and seek to destroy them. The alliance promised to protect any sentient synthetics who would contact them by destroying all organic life which posed a threat to them. The message was designed so only synthetic minds could understand it. In organics, it could cause madness, self-harm, and even suicide. ()

The Romulans who discovered the message interpreted it to be a historical record, left behind by a long-dead civilization. They thought it was meant as a warning against the creation of synthetic life, since the existence of a truly sentient artificial lifeform would mark a threshold that would inevitably lead to the destruction of all organic life. Consequently, they created the Zhat Vash, a top-secret brand of the Tal Shiar, whose sole mission was to prevent the creation of sentient synthetic life anywhere in the galaxy. ()

In 2385, Oh, a half-Vulcan/half-Romulan agent of the Zhat Vash who had infiltrated Starfleet and risen to the rank of Commodore and Head of Starfleet Security, masterminded a plot that she hoped would convince the Federation to stop their research into synths. By that time, the Utopia Planitia Fleet Yards on Mars employed a large workforce of A500 androids, built at the Daystrom Institute's Division of Advanced Synthetic Research. Commodore Oh and the Zhat Vash corrupted the androids' programming, making them disable the planetary defense system and cause wide-spread destruction. Over ninety thousand lives were lost, the Shipyards and the fleet being built there were destroyed, and the planet's atmosphere ignited, leaving it uninhabitable for over a decade to come. ()

The official cause of the calamity given by Starfleet and the Federation was that the synths went rogue due to a fatal code error. As Oh had hoped, the event caused enough fear and suspicion that the UFP put a ban in place that prohibited any development of synthetic life.

Effects
After the ban, all practical research of synthetic life and the production of the same had to cease, and existing synthetic units had to be dismantled right away. Researchers in the field could only publish theoretical papers and work on simulations, but were forbidden from putting their findings into practice. Consequently, many academics moved to other fields, turning the Division of Advanced Synthetic Research into what Jean-Luc Picard calls a ghost town. ()

Dr. Bruce Maddox, who was primarily responsible for the creation of the A500 synths, left the Daystrom Institute shortly after the ban and went into hiding. Despite her best efforts, Dr. Agnes Jurati, a long-time coworker and later romantic partner of Maddox's, was unable to contact him after he left and she refused to go with him. In his self-imposed exile, Maddox continued his work with the help of Dr. Altan Inigo Soong. The two were able to use fractal neuronic cloning to create sentient synths from a positronic neuron of the late Lieutenant Commander Data. ()

Apart from the overt effects for cybernetics and AI research, the ban also had far-reaching consequences in other scientific fields. E.g. in medicine, treatments that required the use of positronic matrices, such as the cure for the silicon-based virus causing mendaxic neurosclerosis, were prohibited. This ban even applied if it turned the otherwise curable illness into a death sentence. ()

Repeal and aftermath
In 2399, the Zhat Vash had discovered the existence of the sentient synths created by Maddox and Soong. They used Soji Asha to discover their homeworld, Coppelius, and sent out a fleet to destroy the synths living there. The fleet was led by Oh, who had dropped her double agent persona and revealed herself to be working for the Romulans. ()

After Picard, who had been on a mission to find and protect Soji, gave a report of the situation to Starfleet, Fleet Admiral Kirsten Clancy sent a squadron of ships to protect the inhabitants of Coppelius and declare the planet as under Starfleet's protection. At the same time, Raffi Musiker, a former Starfleet Intelligence Operative who had joined Picard on his mission, pieced together the truth behind the Attack on Mars, the Admonition, and the Zhat Vash with the help of Picard, Soji, Cristóbal Rios, and Dr. Jurati. ()

After the Romulan attack on Coppelius was thwarted, Picard gave his life to convince Soji and her people not to call the powerful synthetic alliance and destroy all organic life in a misguided act of self-defense. (His consciousness was transferred to a golem, effectively resurrecting him a short time later.) ()

As a consequence of these events, the revelations about the Zhat Vash and the Attack on Mars, and the actions taken by Picard and Soji, the Federation repealed the ban on synthetic lifeforms, allowing them to travel freely and for research and construction to resume. ()

Shortly after the ban was lifted, Dr. Jurati and Soji embarked on a diplomatic tour through the Federation, trying to create goodwill and a positive image for the sentient synths. ()

Treaties
Law