The NO says:
10 IPCs if Japan is not at war with the United States, has not attacked French Indo-China, and has not made an unprovoked declaration of war against United Kingdom/ANZAC.
The political situation for USA says:
If the United States has war declared on it by an Axis power, an Axis power captures London or any territory in North America, or Japan makes an unprovoked declaration of war on the UK or ANZAC, the United States may declare war on any or all Axis powers. However, if it’s not yet at war by the Collect Income phase of its third turn, the United States may declare war on any or all Axis powers at the beginning of that phase.
So unless I am mistaken, if UK or ANZAC attack Japan or enter Chinese territory, then any Declaration of War by Japan is not unprovoked. It was provoked by whatever UK or ANZAC did, so Japan can attack UK or ANZAC and unless they declare war on USA or take FIC, the Americans have to stay out of the war until collect income phase of USA’s 3rd turn. In the meantime Japan can fight UK and ANZAC and they get to keep their $10 NO. It’s a good reason for UK and ANZAC to not provoke Japan on round 1 or 2.