World War I
The nation's interest in world peace had already been expressed through participation in the Hague Conferences, and when World War I burst upon Europe, Wilson made efforts to keep the United States neutral; in 1916 he was reelected on a peace platform. However, American sympathies and interests were actively with the Allies (especially with Great Britain and France), and although Britain and Germany both violated American neutral rights on the seas, German submarine attacks constituted the more dramatic provocation. On Apr. 6, 1917, the United States entered the war on the side of the Allies and provided crucial manpower and supplies for the Allied victory. Wilson's Fourteen Points to insure peace and democracy captured the popular imagination of Europe and were a factor in Germany's decision to seek an armistice; however, at the Paris Peace Conference after the war, Wilson was thwarted from fully implementing his program.
In the United States, isolationist sentiment against participation in the League of Nations, an integral part of the Treaty of Versailles , was led by Senator William E. Borah and other “irreconcilables.” The majority of Republican Senators, led by Henry Cabot Lodge, insisted upon amendments that would preserve U.S. sovereignty, and although Wilson fought for his original proposals, they were rejected. Isolationist sentiment prevailed during the 1920s, and while the United States played a major role in the naval conferences for disarmament and in the engineering of the Kellogg-Briand Pact, which outlawed war, its general lack of interest in international concerns was seen in its highly nationalistic economic policies, notably its insistence (later modified) on collecting the war debts of foreign countries and the passage of the Hawley-Smoot Tariff Act.