Final answer:
The United States joined World War I due to Germany's unrestricted submarine warfare, the Zimmerman Telegram, and a desire to protect democracy and freedom.
Step-by-step explanation:
The United States joined World War I primarily because of several factors. One of the main reasons was the unrestricted submarine warfare policy adopted by Germany, which resulted in the sinking of American ships and loss of civilian lives. Additionally, Germany attempted to entice Mexico into declaring war on the United States through the Zimmerman Telegram. Moreover, the United States sympathized with the Allies and wanted to ensure that democracy and freedom were protected.
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