Germans had u-boats and they used these to ensure they had the upper hand in the war. Germans warned that they would attack any boat they saw as a threat, including passenger boats. Many Americans disregarded the threat and still boarded passenger ships. The Lusitania was a passenger ship that many Americans were abroad and the Germans sank it. This angered Americans because the Germans were no killing our people not just sinking commercial boats. We asked Germany to stop sinking our passenger boats but they refused.
In January 1917, the British intercepted a telegram being sent by Germany to Mexico. In the telegram Germany said if Mexico helped Germany defeat the United States then they would help Mexico get their land back from the United States. Although it is argued that the Zimmerman telegram was fake and simply a ploy by England to get the United States involved in the war, it did get the United States involved in the war.
One of the big reasons the United States decided to get involved war Germany's continuance of unrestricted submarine warfare. We asked Germany to stop attacking our boats to respect our neutrality and also respect our neutral rights at sea but they refused. After the sinking of