Forex operates mainly on the concept of "free-floating" The Balay System currencies; this can be explained best as currencies that are not backed by specific materials such as gold or silver. Prior to 1971, a market such as Forex would not work because of the international "Bretton Woods" agreement. This agreement stipulated that all involved economies would strive to hold the value of their currencies close to the value of the US dollar, which in turn was held to the value of gold. In 1971, the Bretton Woods agreement was abandoned. The United States had run a huge deficit during the Vietnam Conflict, and began printing out more paper currency than they could back with gold, resulting in a relatively high level of inflation. By 1976, every major currency worldwide had left the system established under the Bretton Woods agreement, and had changed into a free-floating system of currency. This free-floating system meant that each country's currency could have vastly different values that fluctuated based on how the country's economy was faring at that time.