April 2, 1917: In an address to Congress, President Woodrow Wilson asked for a declaration of war against Germany. Four days later, Congress voted in favor of Wilson's proposal and the United States formally entered World War I.

Wilson's decision to go to war was prompted by Germany's anti-American aggression, including attacks on neutral shipping in the Atlantic and its efforts to help Mexico regain Texas, New Mexico and Arizona if it fought against America. Wilson learned of this through the so-called "Zimmermann Telegram," and the resulting public anger against Germany was such that a declaration of was became inevitable.

As the war began, Wilson asked for volunteers. But he soon realized that larger numbers of troops were needed and signed the Selective Service Act in May 1917. This required men between 21 and 35 to register for the draft, increasing the size of the army from 200,000 troops to 4.3 million by the end of the war. An estimated 116,516 Americans would be killed and 204,002 others wounded during the conflict, which became known — incorrectly — as "the war to end all wars."

Quote of the day

"I not only use all the brains that I have, but all that I can borrow." -Woodrow Wilson

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