Here is the problem….what japan has that starts on mainland asia, in contact with what is china, is sufficent to strangle china, each turn, if you crawl south-west with your infantry and artillery, and china trys to hold the road (logical strategy) then you just choke them. they lose 3 territores a turn, and so long as britain doesnt declare war early, then you just roll over china
as UK you NEED to get china an AA gun, negating the japanese advatage which is:
Japan can win any one fight on the mainland by throwing 10 or so planes in with its land forces.
UK 1 I build an AA gun now, and send one to burma, ready to move it into china when war starts.
Soviet forces on the border with japan could change alot of the mechanics of the china battle. The jap player wont empty korea and manchuria for long, EVEN IF USSR cant attack them untill a condition is met somewhere, just because it feels ackward to leave border territories empty, with 4 or so infantry and who knows what else on the other side.