Why did it take the American people so long to decide to enter the World War I

Around 1910s, US, actually in the post-Rconstruction and the economic getting better than before. American hate the war, and the most progressivism advocated ¡°Isolationism¡±. Meanwhile, the war seemed to be end in nothing. The President Wilson¡¯s election asserted that keep away from war. But the thing changed, in 1915, the Lustain the passenger line of Britian was attacked by German¡¯s U-Boat, killed 1195 people include 128 Americans. Logically, President Wilson asked German, but Germany denied at first.
Meanwhile, lots of international trade ship round-trip on the Ocean, the benefit no longer, because of Ge...