Sit it out, if possible
How about US, are they just gonna sit there while wars are fought all around them? Would US still join the British side of would they stay neutral?
Just as in the historical Great War, I suspect the USA would try to sit the war out. The POD is likely far enough back to butterfly diffiernt politicians into Congress and the White House, so the positions of the politicians with regards to who they favor can't be determined. But the USA was an isolationist nation through most of its history, and would probably stay that way at first.
Now, if provoked, it could go either way, though I would guess the British would have an advantage in courting the USA. Britian can (and likely will) illeagally interdict American trade without killing anyone, whereas the Central Powers can't interdict American ships without U-Boats, assuming that the Royal Navy still rules the waves.
Japan has to be more careful in this one than in OTL. In OTL, Japan could snap up German colonies with little risk...even if the Entente had lost, there's little Germany could do to retake the colonies by force without a much more massive build-up than anything anyone but the USA could manage.
In this timeline, if Japan enters on the side of the Entente, and the Entente looses fast, Russia may well eject Japan from the mainland, or at least force Japan into a weaker position for Russo-Japanese war II. Both sides expected a short war, and a short war that put the rest of the Entente out of action would leave Japan dangling. Japanese experts would probably not expect Austria-Hungary or France to fight on in the face of disaster to save Japan...and the victors might demand a stiff price from Japan for peace.
So--Japan has to be very careful. (And certainly doesn't get in on the side of the Central Powers unless the Entente is seriously coming apart....Japan is too vulnerable to the Royal Navy....and Britian has bases in the area.