Complex sentence: The Emergency Broadcast System (EBS) was an emergency warning system in the United States that replaced CONELRAD, used from 1963 to 1997, when the EBS became the Emergency Alert System.
Split into simpler sentences: The Emergency Broadcast System (EBS) was an emergency warning system used in the United States that replaced the CONELRAD system. EBS was used from 1963 to 1997, at which point EBS was replaced by the Emergency Alert System.