April 6, 1917Reputable sourceWell documented
The United States Enters the War
On the timeline · around April 6, 1917 ·
What happened
Provoked by Germany's resumption of unrestricted submarine warfare and the Zimmermann Telegram, the United States declared war on Germany on 6 April 1917. President Woodrow Wilson framed American intervention as a way to shape a lasting peace.
Why it matters
American manpower, industry, and finance decisively tipped the balance toward the Allies over 1917–18.