The correct answer is C) the massacre of thousands of Armenians by the German army.
Many factors changed the American opinion of the Great War and eventually led to a U.S. declaration of war on Germany. The option that was not one of these factors was the massacre of thousands of Armenians by the German army.
World War I started after the assassination of Austrian Archduke Franz Ferdinand and his wife in Sarajevo. President Woodrow Wilson wanted to maintain the foreign policy of neutrality but the sinking of the Lusitania by the German Navy and the interception of the Zimmerman Telegram made President Wilson change his mind and asked Congress for a declaration of war against Germany on April 4, 1917.