This page contains information regarding Star Trek: Picard, and thus may contain spoilers.
The Aia natives were a theorized advanced space-faring species who lived approximately 200,000 to 300,000 years before the end of the 24th century on the planet Aia. They had the technology for moving stars and of manufacturing advanced synthetic lifeforms. It was assumed that they came to believe there was a threshold in synthetic evolution, that if they crossed that line someone bad would arrive and destroy them. This somebody came from the skies, laying waste to Aia. The survivors, after their world was destroyed, would leave a warning, called by the Romulans the "Admonition", for other species of what not to do. (PIC: "Broken Pieces") However, this conjecture was later proved to be incorrect when the true nature of the Admonition was discovered.