USA had two military alliances of central importance, one with Germany, one with Japan.
The first is to keep Russia in check, the second China.
The rumours of a carve-up, spheres of influence, begin to resonate.
Problem is, you cannot run a country as if it were a business, because to do is to value influence and power above freedom, human dignity, and human suffering.
Japan’s constitution and postwar treaties with the United States constrain their ability to rearm and use military force. Those need to be amended and renegotiated in order for Japan to be an effective ally in the Asia-Pacific region. Japan’s been asking for a change in the status quo for years. Trump is signaling not only a willingness to encourage Japanese rearmament, but a willingness to sell it to the American people in terms of their own interests.
And frankly I wouldn’t be surprised if the same weren’t true of Europe as well. Ever since at least the Obama administration, the US has been begging Europe to increase their defense spending. Aside from Poland, none of them have done so. That might be changing now. Europe didn’t rearm when Obama (whom you actually liked) asked nicely. Getting to sneer at Trump and the United States is a much more effective permission structure. And then the next time we elect a Democrat, Western Europe will give him a Nobel peace prize and pretend the whole thing never happened, just like the last time.