First, a well-functioning international monetary system must impose some form of discipline on national economic policies. In its original conception the Bretton Woods system assumed that the discipline would be based on a set of rules enforced collectively through the International Monetary Fund. Now the enforcement of discipline is entirely left to the markets and this poses several problems.
First of all, its enforcement is far from uniform and symmetric: unsustainable current account surpluses are not sanctioned in the same way as deficits, and the country issuing the dominant reserve currency is largely immune, since it can finance deficits in its own currency as long as other countries are willing to accumulate reserves.