A few years back (when in 15mm mode, so pre 2009) I had built up some 15mm Russian Civil War armies (Red & White generic in my case) and had been using a version of the Peter Pig AK47 rules to play these games!! Mainly using Irregular Miniatures and Peter Pig figures.
I persuaded Mr Kay (of Irregular Miniatures) to do some more Russians, (like the very nice Maxim MG on a gun carriage) so I could game Russo- Japanese War of 1904/05 using my "White" Russians as my starting base and then I added a Japanese army (still sadly unfinished or part done paint job!) from Irregular Miniatures. Mr Kay then added lovely Chinese Civil War figures too, (see http://irregularminiatures.co.uk/
These (not tanks, aircraft or later MGs mind!) can all be used for the First Chinese (or Sino) - Japanese War of 1894–95 which is really 19th century; and of course more in our period is the Second Sino - Japanese War fought between the Republic of China, (now Taiwan only) and the Empire of Japan from July 7, 1937, to September 2, 1945; with the Chinese Communist Forces fighting both; and initially USa volunteers helping out Republican cause (till Pearl Harbour and USA declaring war on Japan); and of course there is the other "Front" on the Battles of (river) Khalkhyn Gol where the undeclared Soviet–Japanese war took place between the Soviet Union, and Japan and "puppet" governments and armies of Mongolia, andd Manchukuo in 1939; the best known and biggest battle being that of Nomonhan. The biggest armour and air offensive in world to that date (probably)??!! You can use lots of WW2 toys to game these later events, or scenarios from same.
The film clips in Richards link are to a part of this war in Manchuria or northern Korea with which I am not familiar (but then my researchs some ten years ago were limited).
Recent web search for this film - The Battle: Roar to Victory (2019) 2h 15min "Action Drama" - clip got following descriptions:
"Over a 4 day period, a fierce battle takes place between Korean independence militias and imperialist Japanese forces in Manchuria, China. The militia includes a master swordsman and an expert marksman."
At https://en.wikipedia.org/wiki/The_Battl ... to_Victory
"In 1920, when Korea was under Japanese rule, the Korean independence forces’ sword-wielding Hwang Hae-cheol (Yoo Hae-jin) and his subordinates such as sniper Byeong-gu (Jo Woo-jin) carried out the operation to deliver funds to the Korean Provisional Government in Shanghai. During the operation Hwang Hae-chul is reunited with Jang-ha (Ryu Jun-yeol), a young squad commander, who has a suicide mission to bait the Japanese forces led by a general (Hiroyuki Ikeuchi) and first lieutenant (Kazuki Kitamura) into Bongo-dong." and "[This] is a 2019 Korean-Japanese period action film, revolving around the Battle of Fengwudong aka Battle of Bongo-dong between Korean independence militias and Japanese forces in 1920."
All interesting grist to mill of little reported histories.