The Agony of Zchol was a battle fought during the Orion War, a war of independence fought by the Orion people against the 58 races signatory to the Treaty of Kammzdast who held them in slavery, primarily the Nine Worlds Confederation.
At the time, Zchol was held by the Kezt, members of the Nine Worlds Confederation. When the Orion War broke out between 94 to 56 BCE (reference stardate -20/94 to -20/56), their Orion slaves rebelled. They sabotaged the Nine Worlds Confederation war effort, kept their ground forces occupied and hindered their space efforts, no matter the risk to themselves. Zchol suffered particularly heavy fighting in a conflict known as the Agony of Zchol.
The Agony left its mark on Zchol. With the conclusion of the war and the golden age of the New Days, Zchol rebuilt, but it was never able to heal all the scars left by the Agony. (FASA RPG module: The Orions: Book of Common Knowledge)