I come from a port city that is very little known outside of china maybe not even inside china, unless you are a sinologist etc...
the japanese couldn't even conquer the port city at the height of their naval power. they control almost all major ports inside china. but for wenzhou.
when you have a determine local opposition with natural defenses such as mountains and locals with butt load of arms. the japanese troops didn't have a good chance.
by the end of the war there from what i remember according to my greatgrand father who fought them. 1 japanese solider hiding on top of the hill next to the city and port. that hill is gone now, the local government decided to dynamite it a decade back to build more sky scrappers.
before we left for the west, some of my elders handed in guns and rifles to the local government.
a local tradition is acknowledge the rulers in the capital and send them their tribute, but we do as we please. this system has been going on since the first imperial unification. unknown to the west and some in china, the reforms really didn't start in the late 70's, but it started in the 50's in wenzhou unofficially off course. the local bosses decided they didn't get the orders from Beijing. some how the orders from the party bosses kept getting lost etc...
it was also a foreign treaty port that had no foreigners. wenzhou would be the american equivalent of Texas and new york city.
this type of chinese locality happens in alot of places. the country is huge, some parts of the country is much better armed and no need to fear from the troops, either communist or nationalist because they were all local. when japanese encounter these type of locals they always had problems.
from what my greatgrand father told me, the local leaders offer them the same deal as they did with the imperials. they get money and locals get left alone. they pretend to be conquered and the Japanese commanders would look the other way and keep marching. the japanese answer the thing with looting all houses of antiques and silver and gold. this didn't go well. locals went to the caves to get weapons and the rest is history.