"The Years the Rice-Paddies were Watered with Blood," was the translated titled of a book I read in sociology class in college (which you'd NEVER know was needed course to be a SOCIAL worker

). I can't remember the author's name - I think the surname was Zhu (not very helpful, I know). It was not just based on Imperial Chinese records, but archaeological studies in sites of former villages utterly destroyed by Kublai Khan's invasion of the Southern Song, as well as the Mongols' own recorded boasts, and witness who were from (and returned to) Vietnam, Japan, Thailand, Burma, and such.
...
I'm sure you must be far better educated and learned on the issue that a Chinese professor and scholar of Chinese Medieval History who has devoted his life to the topic, and has read these old texts (and is fluent in the languages they're written in), and has personally gone to these archaeological sites. Forgive a petulant mortal for doubting the All-Knowing One on the Mountain.