Japan invaded Northern China in June 1937, following the so-called Marco Polo Bridge Incident (or the Lugouqia Incident). The Japanese Imperial Army conquered about a third of the Republic of China within six months, including Beijing and Shanghai, and arrived at the then-capital Nanjing (or Nanking) in December 1937. The Imperial Army had no difficulty in capturing the city since most of Chiang Kai-Shek’s soldiers had already fled. The army immediately began to slaughter hundreds of thousands of Chinese soldiers and civilians. The killings continued for a period of weeks. The number of Chinese murdered remains a controversy to this day: the Chinese allege that more than 300, 000 people were killed and more than 20, 000 women were raped, while some Japanese historians challenge those figures and rightist groups simply deny that the massacre even happened.