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The assassination of Archduke Franz Ferdinand triggered World War I by setting off a chain reaction of diplomatic ultimatums and mobilizations due to the existing system of European alliances. After the assassination, Austria-Hungary blamed Serbia and, with Germany's support, issued an ultimatum and declared war. -
American neutrality in WWI was a policy President Woodrow Wilson adopted to keep the United States out of the conflict. However, maintaining this neutrality was challenged by the diverse ethnic makeup of the population, economic ties to European nations, and German submarine attacks like the sinking of the Lusitania. The combination of German provocations, the Zimmermann Telegram, and Russia becoming a democracy led the U.S. to declare war in 1917.