Answer:
After the assassination of Franz Ferdinand in Sarajevo on June 28th, 1914 Austria-Hungary decided to declare war on Serbia. That is how the Great War started. United States decided to stay out of war, but when Germans sunk Lusitania, a boat carried many American civilians it changed the attitude of population towards the war. Still during the campaign for the 1916 Elections a campaign for one the presidential candidates was He kept us out of War. And so it was. But when Germans continued sinking many ships and boats the Unrestricted Submarine Warfare was at the peak. United States decided to enter the war when famous Zimmerman Telegram was interrupted. On April 2, 1917 Wilson addresses Congress with words that United States have to go to war.