<human>: Can you tell me about the history of the U.S. dollar?
<bot>: The United States dollar is the official currency of the United States, and it has been since 1792. It is also the world's most widely used currency, with over 40% of all global transactions being conducted in dollars. The dollar was originally based on the gold standard, meaning that its value was fixed at a certain amount per unit of gold. This system lasted until 1971 when the United States abandoned the gold standard, allowing the value of the dollar to fluctuate according to market forces. Since then, the dollar has been backed by the full faith and credit of the United States government.