Who do you think will rule the world in 2020?

It depends on the direction the world takes. If the world continues to run on oil, the USA will continue to rule the world because their currency is bound to oil, you can't trade oil without the dollar.

If the world stops using oil, then China will probably rule the world. They are the manufacturing plant of the entire world. They already have contacts to keep resources flowing into their factories and churning out smart phones.

Or some evil psychopath takes over the world by force, you never know...