The changing conditions at home and abroad made U.S. participation in world affairs after the Civil War (1861-1865) not only more extensive but vastly more significant. The question of when the United States first became a great power is open to debate. That status may date from the Spanish-American War (1898) or from the U.S entry into World War I (1917).
1914-1920
Wilson's Fourteen Points
The immediate cause of America’s entry into World War I in April 1917 was the German announcement of unrestricted submarine warfare, and the subsequent sinking of ships with Americans on board. But President Wilson’s war aims went beyond the defense of U.S. maritime interests. In his War Message to Congress he declared “our object is to vindicate the principles of peace and justice in the life of the world.” Wilson used several speeches earlier in the year to sketch out his vision of an end to the war that would bring a “just and secure peace,” and not merely “a new balance of power.” He then appointed a committee of experts known as The Inquiry to help him refine his ideas for peace. In December 1917 he asked The Inquiry to draw up specific recommendations for a comprehensive peace settlement. Using these recommendations, Wilson presented a program of fourteen points to a joint session of Congress on January 8, 1918. Eight of the fourteen points treated specific territorial issues among the combatant nations. Five of the other six concerned general principles for a peaceful world: open covenants (i.e. treaties or agreements), openly arrived at; freedom of the seas; free trade; reduction of armaments; and adjustment of colonial claims based on the principles of self-determination. The fourteenth point proposed what was to become the League of Nations to guarantee the “political independence and territorial integrity [of] great and small...