From 1931, China and Japan had been embroiled in a number of small-scale conflicts that had seen vast swathes of territory being occupied by the Japanese.
On 7 July 1937, the Japanese engineered the Marco Polo Bridge Incident, which led to the fall of Beijing and Tianjin and the start of a de facto state of war between the two countries.
This force then moved south, landing an expeditionary force to take Shanghai and from there drive west to capture Nanjing.
This fully illustrated book.
Osprey Publishing Shanghai and nanjing 1937: massacre on the yangtze, paperback/benjamin lai
