美元为什么跌？这个问题涉及到全球经济形势、货币政策和政治因素等多个方面。以下是对这个问题的解析以及英文翻译对照：

首先，美元的下跌往往与全球经济一体化和贸易关系有关。在全球经济一体化的背景下，各国之间的贸易和投资联系日益紧密，货币之间的汇率波动也会相互影响。当其他国家的经济增长强劲或者货币汇率上升时，全球投资者可能会寻求将资金投入这些国家的市场，从而推高美元汇率。英文翻译为：Firstly, the decline of the US dollar is often influenced by global economic integration and trade relationships. In the context of global economic integration, the trade and investment relationships between countries are becoming increasingly interconnected, and the exchange rate fluctuations between currencies also influence each other. When other countries' economies perform well or currency exchange rates rise, global investors may seek to invest their funds in these countries' markets, thereby driving up the exchange rate of the US dollar.

其次，美元的下跌还受到美国国内经济表现的影响。当美国的经济增长乏力、失业率上升或者通货膨胀加剧时，投资者可能会减少对美国市场的投资，从而降低美元汇率。此外，美国政府和央行的货币政策也可能影响美元汇率。英文翻译为：Secondly, the decline of the US dollar is also influenced by the domestic economic performance of the United States. When the US economy performs poorly, the unemployment rate rises, or inflation increases, investors may reduce their investments in the US market, thereby driving down the exchange rate of the US dollar. In addition, the monetary policy of the US government and the Federal Reserve may also affect the exchange rate of the US dollar.

此外，政治因素也可能影响美元汇率。例如，如果美国出现政治动荡或对外关系紧张，可能会导致投资者对美元的信心下降，从而降低美元汇率。英文翻译为：In addition, political factors may also affect the exchange rate of the US dollar. For example, if there is political unrest or tense foreign relations in the United States, it may lead to a decrease in investors' confidence in the US dollar, thereby driving down its exchange rate.