1917 changed all of that.
Admiral von Holtzendorff wrote a memo in December 1916 which argued that unless the Germans cut off Britain from supplies, they'd lose the war. Further, they would need to sink at least 600,000 tonnes of shipping a month to accomplish this. Holtzendorff also reassured the Kaiser not to worry about the American response, promising him that 'not one American will land on the continent.'
The Kaiser signed the order for Unrestricted Submarine Warfare on 1st February, 1917, and it was initially successful, with German U-Boats sinking 500,000 tonnes of shipping in February and March. This extracted a huge toll on American ships importing goods to Britain, and resulted in America declaring war on Germany on April 6th, 1917.