1917: April 6
On April 6, 1917, the United States declared war on Germany. Despite the strong anti-war sentiment in Woodrow Wilson’s government, a combination of events drove the joint houses of Congress to approve the declaration of war against Germany. The May 1915 sinking of the Lusitania ocean liner first caused consternation when it was torpedoed killing 1,198 civilians, including 128 Americans. America demanded reparations and an interdiction against attacking unarmed passenger and merchant ships. Germany initially agreed to these demands, but sunk another civilian liner in November, causing the first shift in public opinion against Germany.
Anti-German sentiment increased when, in January 1917, British intelligence broke the code on the Zimmerman Telegram. They discovered that the Germans had offered Mexico the chance to regain some of the territory lost in 1836 to the US. When Britain released this intelligence to the Americans in March, there was gross outrage in American public opinion. To add to the negative press, Germany broke its agreement to halt the policy of unlimited submarine warfare on February 22. The contravention of the Sussex pledge meant that the United States cut diplomatic relations with Germany, and just hours after the decision was announced, Germany sunk the American liner the Housatonic. This deliberate attack prompted America to prepare for war, with Congress passing a $250 million arms appropriations bill.
After the sinking of four more American merchant ships, President Wilson called for a formal declaration of war against Germany. Congress granted his request on April 6.
The first 14,000 American soldiers would arrive in France on June 26.