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In 1914, at the onset of World War I, American Express in Europe was among the few companies to honor the letters of credit (issued by various banks) held by Americans in Europe, because other financial institutions refused to assist these stranded travelers.
In 1914, when World War I started, many people who happened to be travelling could not get at their money, but American Express offices in Europe were among the few companies to honor the letters of credit so that American tourists could get money to travel back home.