You never put all 18 troops on the border. This is certain death. I move three from Amur to Buryatia and three from Amur to Sakha. So if Japan take Amur you can counter. This leaves your 18 Inf safe and allows you to keep your far Eastern territories. It also gives Japan some breathing room so that they will leave you alone and go after China. You can then go after them when you either: Have American reinforcements or have enough troops East. You could also when they leave you go on a suicide attack through Manchuria and Korea and try and get as high an income as possible. i would not suggest this strategy though as when your units get killed Japan get Mech inf and Tanks to blitz through you Eastern territories and you end up having to proetect Moscow from two fronts. Three possibly if Italy join in. Of course since the turn order means you go straight after Germany you could always build your forces but if the Axis powers are smart they would preform a 1-2-3 puch in the following order: Japan, Italy, Germany so you can’t rebuild units you lose until all three powers have attacked.