Initially, the United States maintained a policy of neutrality during World War I, largely due to a desire to avoid entanglement in European conflicts. However, two significant events shifted this stance and ultimately brought the U.S. into the war.
First, the sinking of the British ocean liner RMS Lusitania by a German U-boat in May 1915 killed 1,198 passengers, including 128 Americans. This incident incited outrage in the United States and raised concerns about German aggression at sea, leading to increased pressure on the government to respond.
Secondly, the revelation of the Zimmermann Telegram in January 1917 further escalated tensions. In this secret communication, Germany proposed a military alliance with Mexico should the U.S. enter the war against Germany. The interception and publication of this telegram fueled public sentiment against Germany and contributed significantly to the decision to declare war in April 1917.