D. the sinking of the British ocean liner, Lusitania.
When a German U-boat (submarine) sank the Lusitania in May, 1915, over 1,000 persons were killed, including more than 100 Americans. The passenger liner was targeted by the Germans because they suspected weapons were being shipped to Britain in the cargo hold of the ship.
As an example of American feeling after the Lusitania incident, consider the reaction of Gifford Pinchot. He had been the Chief of the US Forestry Service (from 1905 to 1910) , and was quoted in the New York Times in May, 1915, after he had just recently returned from Europe. He asserted that Americans on the Lusitania (along with other passengers) were killed because an autocratic military empire was trying to dominate nations that were self-governing. His characterization of German intentions would mirror how President Woodrow Wilson later called on the USA to enter the war to "make the world safe for democracy."
