Bring stability, and people learn the mechanisms that works for their society, and overcome surprisingly large differences in type of obstacles. Be it dealing with the vagaries of the free market, or how to maneuver a Soviet-style bureaucracy.
It's in fact almost depressing how little effect even quiet massive political changes appears to have on growth on "just" national level relative to the effects of larger global trends; but an alternative view is that it shows humans abilities to work around messed up political limitations.