The main reason the United States entered World War I in 1917 was the unrestricted attacks German submarines were making on American ships and ships containing American passengers. Additionally, Americans were enraged at a telegram British intelligence intercepted in which Germany sought an alliance with Mexico.Continue Reading
U.S. President Woodrow Wilson at first sought to remain neutral when World War I began in 1914. However, friction with Germany intensified when Germany created a naval blockade of England, hindering its trade with the United States. In 1915, Germany announced that it would attack all ships trying to run the blockade. In early 1915, Germany sank a private U.S. ship William P. Frye, and soon after, it sank the Lusitania, killing 1,201 people, among them 128 Americans. Despite a 1916 pledge to ensure passenger safety, Germany continued to sink unarmed ships, resulting in the loss of more American lives. In 1917, seeking an early end of the war, Germany completely reneged on its pledge and resumed unrestricted attacks on shipping.
Exacerbating the tension between the United States and Germany was the infamous "Zimmerman Telegram" in which the German foreign minister promised U.S. territory to Mexico in return for Mexico's help in the war effort. The story became top news in the American press, helping to convince the U.S. public that war was inevitable. The United States officially entered the war on April 6, 1917.Learn more about World War 1