During the 24th century, the Kes was the larger of the two nations, comprising three quarters of the planet's population, while Prytt contained the remaining one quarter of the population. The two nation-states had a paranoid dislike of each other, bordering on xenophobia.
In 2370, the Kes applied for an "associate" Federation membership, as an exception to the normal rule requiring a planet be unified socially and politically for membership. The application for the admission of Kes to the Federation was rejected due to the unresolved social, political, and military problems between the two nations. (TNG: "Attached")