In the 1960's, American economist Robert Triffin identified what later came to be known as the 'Triffin dilemma'. The Bretton Woods system, so Triffin, that had made the US dollar the world's 'reserve currency' necessitated that the US run a perennial current account deficit in order to satisfy the demand for dollars as a reserve asset (we can assume that the same idea holds for its 'gold-free' successor).