Simplify the following text for a Grade 8 native English-speaking person.
Original: The Nanking Massacre or Nanjing Massacre , also known as the Rape of Nanking , was a mass murder and war rape that occurred during the six-week period following the Japanese capture of the city of Nanjing ( Nanking ) , the former capital of the Republic of China , on December 13 , 1937 during the Second Sino-Japanese War .
Simplified: The Nanking Massacre is a genocide that took place in Nanjing , China during the Second World War .