Remember 1980s'?
When Miracle of the world: Japan, was buying everything in the world! All assets , investing in the USA and etc etc. Japanese trading surplus went from 6 Billion to 200 Billion, so they needed to put those savings somewhere... and USA saw it all. So they are so greedy, and wanted a piece of that ballooning pie... So Forex, fluctuating currency rates were introduced.
I personally don't think that that was an accident.
With control of USA can virtually control their infliation / defilation / debt / export / import and other important factors of Economy. Not to forget they are making money, of money, and thin air.