To make it simple
Japs in the past invaded china, in special, this beautiful city i know called nanjing. The "battle" is known as THE RAPE OF NANJING.
To resume, japs tookover the city and started raping women, killed men, forced kids to have sex with their mothers, dads to rape their daughters, and such.
Theres a girl that wrote a book about this, she ended so shocked that killed herself.
Chineses will NEVER, mark my words, NEVER forgive japaneses for this, and they do want revenge.