Please research the ‘Zimmerman telegram’ and the re-introduction of unrestricted submarine warfare by the Hun in 1917.
A better question is, after the rape of Belgium, the use of chlorine, mustard and phosgene gas, the sinking of the ‘Lustania’, the ‘Black Tom’ terrorist attack, etc., why did the US wait so long to enter the war against the Central Powers?
Simple answer, the largest number of immigrants to the US at that time had come from GERMANY and AUSTRIA. Besides, US industries were able to sell to both sides, though mostly to the Triple Entente, making incredible profits until 1917.
How did US Shipping get past the British Naval Blockade of Germany?
My grandfather was in the Secret Service at the time and was sent to Mexico to check the goings on there in the wake of the Zimmerman telegram.
My GErman ancestors came over, late 1800s, to get away from all the disruption Kaiser Wilhelm was causing. My great-great-grandparents looked at their baby in the cradle and decided “You shall not serve the Kaiser.”