text: The Lawrence Massacre , also known as Quantrill 's Raid , was a rebel guerrilla attack during the U.S. Civil War by Quantrill 's Raiders , led by William Clarke Quantrill , on the pro-Union town of Lawrence , Kansas .
simplified: The Lawrence Massacre ( also known as Quantrill 's Raid ) was an attack on the town of Lawrence , Kansas on August 21 , 1863 .