The US dollar gets some of its value from the awesome US military. Worse comes to worse, we can take stuff from others regardless of how poor we are. Its a self-destructive mode of operation and would be used as a means of last resort. (North Korea is an extreme example - the world pays them not to go crazy with their nukes)

A more positive source of the dollar's strength is the US economy and its resourcefulness and innovation (ie hackers:)