Yes, Fionn, I suppose that common interest describes it better than common purpose. They didn't really act in concert in the way that Germany and Italy did. What I meant was that Germany and Japan (and Italy too) had similar but non-conflicting objectives.

I suppose that a historical reason for their wish for expansion was that, for different reasons, late unification for Germany and Italy and isolationism for Japan, that they had never developed the Empires that other nations had. And now I suppose we'll have a lot of Americans explaining that the USA never had any interest in acquiring an Empire.