In 2116, the people of Zarta were a flourishing race of many millions. Their civilization began experimenting with using machines to replace manual labor, beginning with everyday chores and progressing to farming, policing, business and science. This created a utopia, in which all their needs were provided for them. Around 2166, the machines created the city builder, a machine designed to construct entire cities. However, the city builder began to construct buildings and other facilities on its own. Construction got out of control, threatening the people. Because machines had been responsible for the planet's technological progress for so long, the people did not understand the complexity of the machines currently existing and had even lost knowledge of technology prior to the rise of the machines. When the master agricultural unit broke down, the people began to starve.
First contact between the Federation and the people of Zarta was made in 2266 by Captain James T. Kirk of the USS Enterprise and their leader, Krill. After learning that the the people were threatened with extinction, Kirk and his crew assisted in devising a means to defeat the city builders and reclaim the planet. (TOS comic: "Invasion of the City Builders")