What event(s) led to the United States entering World War I in 1917?

• A. Germany's resumption of unrestricted submarine warfare and the Zimmermann Telegram; combined with allied ties and economic interests.
• B. The Allied victory at the Battle of the Somme.
• C. The Russian Revolution's success.
• D. The signing of the Treaty of Versailles.

Answer: (A)

The main idea here is what pushed the United States to enter World War I in 1917. The strongest combination of factors was Germany’s decision to resume unrestricted submarine warfare, which threatened American ships and lives and endangered U.S. shipping. When Germany declared it would sink ships without warning, it crossed a line that made neutrality impractical and opened the door to war with a nation that was attacking American commerce and citizens at sea.

Adding to that pressure was the Zimmermann Telegram, in which Germany proposed a military alliance with Mexico against the United States. The interception and publication of that message stirred public anger and made the idea of going to war with Germany feel more urgent and justified to many Americans.

These developments didn’t happen in isolation. The United States already had deep economic and political ties to the Allies—shipping vast amounts of money, munitions, and supplies to Britain and France—and a growing investment in an Allied victory. When you combine the maritime threat, the provocative telegram, and long-standing interests in an Allied victory, entering the war on the side of the Allies became the plausible and consequential choice.

The other events don’t fit as the decisive trigger: the Battle of the Somme occurred in 1916 and did not compel U.S. entry; the Russian Revolution, while influential in broader wartime dynamics, did not force the United States to join in 1917; and the Treaty of Versailles was signed after the war, not a reason for U.S. entry.