In the 19th century, it was manifest destiny, Atlantic to Pacific. In the 21st, it's time to go global. The truly great countries are empires!
Just think of the possibilities from Iraq and Afghanistan alone -- we'd be adding 42 million fundamentalists!!! That could ensure GOP control of Congress and the White House for perpetuity, as we'd be adding one state (Iraq) with a population bigger than Texas and another (Afghanistan) the size of Florida!
As for Africa -- we only want new states that can be pillaged for U.S. corporate benefit. Not much of Africa fits the bill. And, except for the Arab states in the north, they'd be damn Democrats!!!!!
Before we make Iraq and Afghanistan states, though, we will need to amend the Constitution so that it applies to only the original 50 states (and maybe while we're at it, subtract some Blue states, too, especially Massachusetts). We don't want a little thing like the Constitution messing us up.