The Kes were one of two Kesprytt states on Kesprytt III and controlled three quarters of the planet. They maintained hostilities with the Prytt, a nation-state controlling the other quarter of the planet, but who were of the same species.
In 2370, the Kes applied for associate Federation membership. While the Federation was wary of accepting a planet that had yet to be unified, they sent the USS Enterprise-D to investigate. The Kes invited Doctor Beverly Crusher and Captain Jean-Luc Picard on a diplomatic mission to their territory, but the Prytt kidnapped them, believing their purpose was malevolent.
The Prytt had no ambassadors, no emergency contact procedures, nor indeed any means of contacting the Kes. The last official diplomatic contact between the two parties took place almost a century prior to the incident; more recent, less formal contacts (which the Kes were not at liberty to discuss with the Federation) made little progress toward peace. Whereas the Prytt were extremely reclusive and xenophobic, decades of ongoing conflict with them had made the Kes deeply suspicious and paranoid, leading them to believe that the Federation was secretly collaborating with the Prytt. When Kes and Prytt dignitaries met aboard the Enterprise-D to discuss the fate of the two prisoners, so many wild conspiracy theories and childish arguments were leveled by each party against the other that Commander Riker quickly lost interest in the negotiations.
When the doctor and captain were rescued, they recommended to the Federation that they deny the Kes' application until the Kes and Prytt were unified. (TNG: "Attached")