If you look at the focus tree there are options in the diplomatic tree to deal with the warlords. Or, assuming that WT is high enough, just boot and fabricate against them. Be aware that might cause them to join another faction.
After you control China you have to decide what to do, attack the Soviets, finish Japan, or go after Allies. Each will require planning as they will be ahead of you in tech.
Be warned, just because you peaced out Japan doesnt mean they wont be back or that you can't go after them if you want. I have gpne both ways, took the option to peace out and told Japan it is war to the death. Like continuing to fight better so far, I kept Korea.