History of North America

What prompted the United States to enter World War 1?

The United States' entry into World War I was largely prompted by the Zimmerman Telegram, a secret diplomatic communication sent from Germany to Mexico during the war. Intercepted and decoded by British intelligence, the telegram revealed a German proposal for an alliance between Germany and Mexico, offering Mexico return of territories lost in the Mexican-American War in exchange for Mexico launching attacks against the United States and its allies. The news of this proposed deal and potential interference in the Western Hemisphere by Germany led to widespread outrage and support in the United States for joining the war against Germany.