The Galactic Army of Light was a rag-tag group of individuals who inhabited the planet Nimbus III. They were recruited by Sybok, in 2287, to serve his needs, as he prepared for his final leg of his journey to locate Sha Ka Ree. J'onn was a "soldier" in the Galactic Army of Light.
Using his Army, Sybok captured the capital settlement, Paradise City, whereafter they took hostage the three representives of the city -- the Romulan's Caithlin Dar, the Klingon's General Korrd, and the Federation's St. John Talbot -- in attempt to acquire a starship.
Sybok and his followers were able to hijack the USS Enterprise, which they later took beyond the Great Barrier. (Star Trek V: The Final Frontier)