Spain's American empire began as the serendipitous outgrowth of the search for a shortcut to China. That search derived from two mid-fifteenth-century developments: the Ming Dynasty's decision to adopt a silver standard for its medium of exchange and the Ottoman Turks' capture of Constantinople in 1453. China's great demand for silver and the disruption of the Silk Road drove the need to find alternative access to China. King John II of Portugal...