At least as of 2374, the Kraylor were involved in a conflict with the Annari Empire, and in that year the Annari erected a blockade around the Kraylor homeworld. Though a shield grid protected the planet from a direct attack, the planet was slowly choked to death because it was dependent on external sources for food and medical supplies, and it was almost impossible to get ships trough the blockade in the following three years.
As of 2377, Kraylor scientists were in the process of developing cloaking technology at a secret off-world base, and in the same year the Nightingale, a prototype ship capable of cloaking as well as carrying key scientist, was able to reach the homeworld with the assistance of USS Voyager Ensign Harry Kim. Even though the Annari found a way to detect cloaked ships using specially-designed scanning pulses, the mission was considered a success and soon cloaks were installed on other ships, enabling the Kraylor to escape the blockade. (VOY: "Nightingale")