The best thing I have found that keeps Japan in check is having the US Build a factory in Alaska and place navy armada in seazone 64.
This does a couple of things:
Bombers placed in Alaska can strategic bomb Japan.
The US can threaten to invade Japan during the next turn.
The US can land units in Russia and threaten Japans Asia control.
Most importantly it forces Japan to keep buying a navy instead of ground units in order
to protect Japan.