Woodrow Wilson became the first United States president to travel abroad in office when he went to Paris in 1918 to attend the Paris Peace Conference to end World War I. It was while he was in Paris that he also campaigned to create the League of Nations, the precursor to the United Nations. Wilson was actually responsible for a lot of U.S. presidential firsts — he was the first president to earn a Doctor of Philosophy degree, the first president to make a speech on the radio and the first president to attend professional baseball's World Series. Also, the first federal income tax was levied during his time in office.
More U.S. presidential firsts: