That’s just crazy. If ANZAC declared war on Japan by themselves, without bringing UK Pacific or USA into it, ANZAC would cease to exist in 3 or 4 rounds and Japan would have an extra NO, another Victory City and be close to a second NO (the 5 of 7 Islands NO).
Okay, say on J1 Japan just messes around with China and does some building. Then A1 ANZAC decides to attack Japan all by their little selves and you move your little navy to SZ 54 and all 3 of your fighters to Queensland so they can scramble. On J2, Japan moves the bulk of it’s MASSIVE navy to the base on the Carolines and build transports & equipment on Japan. On J3 they come down to SZ 54 and smash the little ANZAC navy and the 3 fighters and probably invade and take Queensland while moving those transports filled with men and equipment to the Carolines. On J4, they move the transports on the Carolines down to invade New South Wales along with the huge navy to smash anything that ANZAC managed to put there, with the forces already in Queensland, and ANZAC is out of the war. On J5, they will have to turn around and deal with USA by now, probably by sending their navy steaming toward Hawaii or back up to the Carolines while the land forces spread out and take the rest of the ANZAC territories.
Total suicide for ANZAC. They are too small. They need the help of India and USA to deal with Japan. Thus the term “Allies”. You can’t take on a mean-a** aggressor all by yourself.