Possibly the Most Important Numismatic Book of the Decade Well before the United States entered World War II, copper, nickel and several other metals had assumed strategic importance. All were necessary for Americas restoration of military competence, and European war pressures quickly pushed the U.S. into becoming the manufacturing arsenal of democracy. Canadian and U.S. copper and nickel mines could not increase production fast enough to meet manufacturing demand. During the early months of the war, no one knew if there was sufficient strategic material to produce the massive quantities of weapons and other supplies required to fight the Japanese and Germans and supply the allies.