The United States entered WWI because of what factor?

• A. Zimmerman Telegram
• B. German submarine warfare
• C. Sinking of the Lusitania
• D. British blockade

Answer: (B)

Unrestricted submarine warfare by Germany is the factor most directly connected to the United States entering World War I. When Germany declared it would sink ships bound for Britain without warning, American ships and lives were put at immediate risk, and U.S. merchants and citizens faced real peril on the seas. This aggressive challenge to neutral rights and to the safety of American commerce made war feel like the necessary response to defend national interests and ensure safe passage for American trade.

Earlier events like the sinking of the Lusitania heightened anti-German sentiment, and the Zimmermann Telegram revealed German plans to ally with Mexico, influencing public opinion. But the decisive shift came from Germany’s renewed submarine campaign in 1917, which directly provoked the decision to seek a formal declaration of war. The British blockade worsened tensions, but it was Germany’s submarine policy that finally forced the United States to enter the conflict.