Complex sentence: At its inception, the AMS represented all students attending Queen's University; however, that changed in 1981 when the Graduate Students Society, an AMS member society formed in 1962, voted by referendum to secede from the AMS.
Split into simpler sentences: At its inception, the AMS had represented all students attending Queen's University. However, that changed in 1981 when the Graduate Students Society, an AMS member society formed in 1962, voted by referendum to secede from the AMS.