What German war policy precipitated US involvement in WWI?
The United States originally wished to remain neutral when World War I broke out in August 1914. However, it insisted on its right as a neutral party to immunity from German submarine attack, even though its ships carried food and raw materials to Britain. In 1917 the Germans resumed submarine attacks, knowing that it would lead to American entry. When the U.S declared war, the U.S. army was still small by European standards and mobilization would take a year. Meanwhile, the U.S. continued to provide supplies and money to Britain and France, and initiated the first peacetime draft. Industrial mobilization took longer than expected, so divisions were sent to Europe without equipment, relying instead on the British and French to supply them.