Why was 1917 a pivotal year for both Germany and the Allies during World War I?

1917 was
the fourth year of the Great War, and during the timeline of this year, many important events
took place that impacted both Germany and the Allies. One of the most significant events in
January 1917 involved a telegram sent from the Germans that was intercepted by British
intelligence forces; the British were able to alert the Americans that Germany was proposing a
deal to Mexico that promised Mexico the states of Texas, Arizona, and New Mexico if Mexico
fought against the US on the side of Germany. The revelation of the Zimmerman note led directly
to the decision of the United States to declare war on Germany in April 1917. In June of 1917,
American troops begin to arrive in France.

Other important events that
involved both sides of the war include significant battles at Ypres, a declaration of war by the
US on Austro-Hungary, and an important win for the Allies at the Battle of Cambrai. During this
battle, the British successfully surprised the Germans with a tank attack, revealing that the
Germans were in fact vulnerable in places and boosting morale.