A world currency typically refers to a specific currency used by investors and others to conduct international trade. World currencies have evolved from gold in the mercantilist period of the 16th century to the U.S. dollar in the 20th century. These currencies are held in reserve by businesses and governments to surmount barriers to foreign trade. Nations that are responsible for printing world currencies are often seen as possessing monetary hegemony or control over the global economy. Critics of monetary hegemony have suggested a single global currency to replace currencies printed by individual nations.