The Rebellion was a period of period of strife and uprising experienced within the Silo over one-hundred-forty years prior to the events of the series. During the Rebellion, a group of rebels stormed the top of the Silo in an attempt to open the door to the Outside in order to poison the entirety of the Silo. Their attempt was eventually thwarted, however.
During the events of the Rebellion, the Rebels destroyed much of the knowledge the Silo held, such as books and computer drives; as a result, much of the knowledge of the Before Times is lost. The Silo celebrates the victory over the Rebels each year on Freedom Day.[1]