The first paper currencies were notes redeemable for gold or silver, or warehouse receipts for stored gold. Eventually, the receipts themselves were exchanged, and became currency in common usage.
The link to precious metals became less concrete. As governments needed to buy votes or finance wars, they yielded to the temptation of printing more notes than there was gold or silver to back them, and inflation resulted.
The process of currency destruction has accelerated, particularly since 1971 when the US closed the gold window, and stopped exchanging dollars for gold. In the last 10 years, the Fed has printed trillions of dollars backed by nothing at all at the fastest pace in history, a move that has driven the prices of precious metals skyward.
Meanwhile, gold and silver are in short supply. Twenty-two years of low prices has resulted in a dearth of production and exploration, while industrial applications for silver have soared.
China and India are enjoying a burst of capitalist prosperity, and have historically turned to precious metals for wealth preservation.
COMEX futures positions in silver, much of which must be covered by deliveries or purchases, are estimated to be equal to or greater than all new productions.
Think of gold as large denomination money, and silver as small change: while a 1-ounce gold coin now costs about $650, a roll of 90% silver dimes is a mere $50. Ruff predicts that silver will eventually be more profitable than gold by at least 100%.
Read The Case for Buying Silver: A History of Paper Money by Howard Ruff