Why did the Japanese army avenge themselves on Chinese

[Kenny同志]

I can't make out the reason provided by the man in this 3-minute video [the last one at the bottom] for the Japanese army's vengeance on Chinese in Nanking.

I'd appreciate it if you're kind enough to do me the favour of watching the video and telling me the reason.

[Koxinga]

The Chinese won a few battles in Shanghai and the Japanese were humiliated. There were many westerners who owned cameras and recorded the Japanese humiliation. That provoked the Japanese who wanted to regain their honor by being brutal in their invasion.

I don't have a lot of knowledge about those events, but that's what I understood from the video.

[Kenny同志]

Thank you very much, 克羅地亞的同志.