Japan has less than half of the US (or Euroland) population and insignificant natural resources. Its GDP is way behind that of the US, China, and Euroland. (However, it does beat California, not to mention Texas.)
An economic union of the reasonable Asian countries could be big enough but what would China do?
So what does population have to do with it? I thought we're talking about economic strength.
Also way to compare apples to oranges eg the whole of a country to the 2nd highest producing state of the United states.
If we were to make this assumption true, then we would have to compare apples to apples, 2nd highest producing state to 2nd highest producing state (based on a per capita basis)... in which case Western Australia would beat Texas hands down. (nearly $61k USD per person compared to about $41k USD per person)
So while the biggest topic of discussion with the American's seems to be just the financial crisis, Australia is experiencing a weird dichotomy, financial crisis and resource-driven economic boom at the same time.
You kinda forgot about Japan & Australia, if all those things happen I would bet that either of the two would become a standard.
Being an Australian I would like to say us, but it would no doubt be the Yen.