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 have a paranoid dislike of each other, bordering on xenophobia.
In 2370, the Kes applied for a special "associate" Federation membership, as an exception to the normal rule requiring a planet to have a united planetary government for membership. The application for the admission of Kes to the Federation was rejected due to the severe diplomatic and military problems between the two nations. (TNG: "Attached")