Funny in my current CORE game I have the opposite problem.
Its April 1942, I am Japan and part of the Axis. Only Britain and Canada remain as Allies and Britain both hold onto their mainland only (even Belfast has fallen to Italy!). As Japan I have annexed, puppeted or occupied China, Sianking, Siam, Holland (with German help), Belgium (with German help), South Africa, Australia, New Zealand, India, Iraq, Syria, Egypt and I also have Gibraltar.
The Soviet Union is all but completely collapsed, they have 200 divisions left but have lost Leningrad, Moscow, Stalingrad from their western front and Vladisvostok and Irkutsk from their Eastern front.
The USA have had a war entry of 100% for at least 12 months, but nothing. I do not want to DoW them as it would be far too gamey - I have nothing to gain from it other than the challenge of defeating them (I think along the lines of war being a continuation of politics - and I would have no ambitions to occupy the USA!)
I know they will enter the war when the British Isles are finally taken, but by then I think it will be too late for them to have any real impact at all on the Axis.