The United States joined World War I for several key reasons, including:
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Unrestricted Submarine Warfare: Germany resumed its policy of unrestricted submarine warfare, which threatened American ships and lives. The sinking of ships like the Lusitania, which resulted in the deaths of American citizens, heightened tensions.
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The Zimmermann Telegram: In early 1917, British intelligence intercepted and revealed a secret communication from Germany to Mexico proposing an alliance. The telegram suggested that Mexico should join the war against the U.S. in exchange for the return of territories lost during the Mexican-American War. This revelation outraged Americans and stirred public support for joining the war.
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Economic Interests: The U.S. had strong economic ties with the Allies, particularly Britain and France. American banks had loaned significant amounts of money to the Allies, and a victory for the Central Powers could jeopardize these financial interests.
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Cultural and Ideological Factors: Many Americans felt a cultural affinity for the Allies, particularly Britain and France. There was also a prevailing belief in promoting democracy and protecting it against autocratic regimes, as represented by Germany.
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Propaganda and Public Sentiment: British propaganda effectively shaped public opinion in favor of the Allies, and many Americans were emotionally compelled to support their cause.
These factors collectively led to the U.S. declaring war on Germany on April 6, 1917.