Having nearly exhausted local populations and resources in the US itself, the empire is now moving on to the rest of the world - which is exactly what globalisation is about, and has always been about.

A lot of what the US 'exports' is really manufactured elsewhere. Counting it as an export is something of a financial fiction, because often it's really a re-export - physically the item may not go anywhere near the US at all.  

When I buy an iPod it's counted as a US export, even though it's made in China. The reason is that most of the value remains with Apple, while China receives a small proportion of that income for manufacturing and logistics management.

Wall Street will continue to appear to levitate as long as this continues - i.e. either until there's a crisis of confidence, or the supply of assets and energy from the rest of the world starts to dry up. Effectively it's an international market, not a national one, and most of the accumulated wealth is not being shared with the US as a whole - just with a small share-owning sub-stratum of US society.

Workers in the US, meanwhile, are being kept out of the wealth loop, because when manufacturing happens off-shore, they don't get paid. (Or rather - they don't get employed, never mind paid.)