The currency is not any longer the safe and stable currency it once was. Changes within the global economy and other sectors of society have made it a but optimal choice for investment. This is no means the currency is finished. The devaluation of the currency went on in many steps. Most of them are tiny and now have added up to large leaps. There are, however, some major events that have taken chunks out of the dollar's value. One is when the govt took us off the gold standard. This meant that gold was not backing up the dollar, simply the credit of us, the primary step during a long road of the devaluation of the dollar. 

Investors began doing business in other currencies once they had previously used the dollar. This is often becoming a hot topic in international financial markets, especially with us facing a multi-trillion currency shortfall. Those seeking to be financially secure will had best to think about investing in those commodities that have stood the test of their time and whose current prices keep rising. Gold and silver are potential investments that are around longer than the currency and still rise in value year after year. This suggests they continually show returns, regardless of what the currency or the other fiat currency is experiencing. Facts like these make the question of "should I buy gold or silver rather than investing within the dollar?" much easier. 

In the end, economic investments in monies and other politically controlled tools are highly unstable sometimes and ultimately put investors at the whim of any number of forces working towards bitcoin transactions. When these currencies have long gone or changed or have all been digitized, there still are going to be gold and silver, and that they still are going to be favorites of humanity and a key to being financially secure.