Well the USA does have the best economic hitmen. Britian has some good imperialistic training in those matters too.
So who will win the currency war game? Seems like USA and Britain. Yet Japan as a lapdog will be really hurt if their 20% sucess is not allowed to stick. And Europe could blow up, with significant effect all around, if they aren't allowed to decimate their currency. What a tangled web they weave.
It may become a "take turns" pop a mole strategy or end effect.