Why did the United States go to War in 1917 against Germany? How did the United States get involved in a war started by the assassination of an Austrian archduke? Between the sinking of the British luxury liner Lusitania in May 1915 and April 1917 Americans engaged in a bitter debate over how to respond to Germany's attempt to seal off Great Britain from the United States with submarines. The most prominent advocate of war was ex-President Theodore Roosevelt. The most prominent advocate of neutrality was Senator Robert M. La Follette. Both castigated President Woodrow Wilson for seeking a middle ground. After the war Americans became disillusioned about what had been won. Many came around to the La Follette view that American intervention had been a mistake. This view persisted until the Japanese bombed Pearl Harbor in 1941 and their ally Hitler declared war on the United States.