Besides the end of slavery and democracy, another modern sign of progress is the idea of territorial integrity. This is what makes it impossible for the US to do what Britain did, i.e. acquire colonies around the world and force them to keep paper sterling as reserves. The world simply won't allow it.
Ensuring that barrels of oil are sold for USD (thus creating a merket therefor) effectively makes oil consumers (i.e., the world) a "slave" (i.e., they don't receive compensation specifically for their contribution) of the U.S. economy.