This document summarizes the key factors that led the United States to initially remain neutral in World War I but eventually enter the war in 1917. It discusses the economic reasons for neutrality due to American loans to the Allies. It also describes the human toll of the war and President Wilson's support for neutrality. However, two events changed American sentiment: the sinking of the passenger ship Lusitania, which killed over 100 Americans, and the intercepted Zimmerman Telegram, in which Germany tried to enlist Mexico as an ally against the U.S. These events increased support for entering the war.