Japan's constitution--written by the US, following WWII--forbids the country from acquiring military weapons, beyond those needed for pure self-defense.
In the mid-1940s, this probably made good sense.
Now...well, much less so, I think.
Japan could act as a serious counterbalance to an increasingly aggressive (and expansionist) China--if only it were allowed to do so.
Remember: We fought against Germany and Italy in WWII also; but we do not wish to constrain them in this manner.
Thoughts?