In the mid-24th century, the Angosians were involved in a protracted conflict called the Tarsian War. Being inherently non-violent, the Angosian authorities were forced to subject their soldiers to genetic engineering and chemical manipulation in order to successfully end the conflict. However, it was discovered that the process was irreversible, and when the war ended, the "super soldiers" were unable to function within or co-exist alongside the normal population of Angosian society, and as such were confined indefinitely to a penal settlement on an Angosian moon, Lunar V, and considered to be outcasts and criminals.
In 2366, the Angosians petitioned to join the Federation. The USS Enterprise-D visited Angosia III to follow up the petition. However, the occasion was interrupted by the escape of the soldier Roga Danar who was pursued by the Enterprise crew at Angosia III's request. Unfortunately for the planet, while the crew was successful capturing him, they then learned from him of the gross systemic sentient rights violation being committed.
While Captain Jean-Luc Picard found that the Angosian government refused to discuss the concern, Danar escaped and proceeded to start a rebellion with his fellows. In the face of the planet's unacceptable policies and the resultant civil upheaval caused by them, the application was put on hold for the immediate future. (TNG: "The Hunted")