America entered World War One on April 6th, 1917. While America tried to keep out of the War – though she had traded with nations involved in the war – but unrestricted submarine warfare, introduced by the Germans on January 9th, 1917. It was the primary issue that caused Woodrow Wilson to ask Congress to declare war on Germany on April 2nd. Four days later, America joined World War One on the side of the Allies.

Isolationism refers to America's longstanding reluctance in being involved in European alliances and wars. Isolationists made the view that America's perspective on the world was different from European societies and America could advance the cause of freedom and democracy other than going to war.