In the 19th century, during the glory days of the British Empire, the pound sterling reigned supreme in a world that accepted it as the universal medium of global exchange. But as the wars of the 20th century took their toll on the fading United Kingdom, the U.S. dollar became ever more important, officially supplanting the pound as the world's dominant currency at the 1944 Bretton Woods Conference. It has been the global reserve currency ever since. But how long it can maintain that lofty status depends both on the continued strength of the United States and the status of any potential successor currencies. ...