Anyone have any links to authenticate what actually did happen?
The best book I have read on this is 'The Rape of Nanking' by Iris Chang - it is well worth a read . Some of the photographs should convince any doubters.
That looks more like the tail end of the Civil War, late 40s rather than 30s. The captions make mention of President Li Tsung-Jen (who incidentally proved it was possible for Chinese armies to defeat Japanese ones after all), yet he didn't become President of the Republic until 1947 or thereabouts.
did you check out the other films on the link